ASPE CPD STUDY QUESTIONS AH 100% VERIFIED ANSWERS 2024/2025 CORRECT STUDY SET, Exams of Water and Wastewater Engineering

Download ASPE CPD STUDY QUESTIONS AH 100% VERIFIED ANSWERS 2024/2025 CORRECT STUDY SET and more Exams Water and Wastewater Engineering in PDF only on Docsity! ASPE CPD STUDY QUESTIONS AH 100% VERIFIED ANSWERS 2024/2025 CORRECT STUDY SET Front Back What is the specific weight of water? 62.4 lbs per cubic foot What happens in a storm and sanitary system after it passes the water test? A smoke pressure test is recommended with a smoke pressure of 1 in wc to prove the system gas tight. Is an air test acceptable for a storm and sanitary system? Yes, if a water test is not possible, at a pressure of 5 psi, are tests are impractical and costly What are the testing procedures for the storm and sanitary system? A water test upon completion of the rough piping and prior to concealment of 10 ft wc minimum (except the topmost 10 feet of pipe), not to exceed 100 ft wc. If system is higher than 100 feet, test plugs must be installed to facilitate testing, rarely are more than 7 stories tested at one time. A peppermint oil test may also be done with 2 oz of peppermint oil and 10 qt boiling water, and searching for peppermint smell at leaks, however it is difficult to pinpoint the leak by this method The maximum length from the vent connection to any future drain outlet is required by code, why, how long is the distance (listed in the book), and what’s the exception? To prevent a dead end where slime, sludge and fungi can grow, 2 feet, unless the piping must be extended to an accessible location for a cleanout A sanitary tee may be used in the vertical but what may not be used in the vertical and why? A double sanitary tee because the possibility of flow crossover and excessive pressures when one branch is discharging and the other isn’t are possible What are the slopes of pipe inside the building that correspond to 2 fps velocity? 1/4 in per foot for 3 in and smaller 1/8 in per foot for larger pipe all elbows, taps, tees etc are tapped at a pitch of 1/4” per foot Where should cleanouts be provided? 1) Inside or outside the building at the point of exit (use a wye branch) 2) at every change in direction greater than 45 degrees 3) every 50 feet for piping 4” and less, and 100 ft for larger piping 4) underground piping larger than 10 in should be provided with manholes at every change in direction and every 150 feet 5) at the base of all stacks 6) as required by code What size cleanouts are provided in piping? Piping up to 4 inches, the cleanout is the same size as the pipe. Piping greater than 4 inches, 4 inch cleanouts are adequate. What should be installed in the house drain if there is a danger of backflow of sewage into the building? Whats the difference? A backwater valve or a combination BWV with manually operated gate valve. The BWV does not interfere with the airflow throughout the system, and the gate valve is recommended where there is a history of backflow as a positive means of protection. Branch connections to the house drain should be made where and why? At the upper portion of the pipe (above the 1/2 - 2/3 full mark) because: 1) there is a lower chance of stoppages in the branch 2) there is less flow interference at the point of connection 3) When there is no flow in the branch, the full area of the pipe is available to relieve pneumatic pressure fluctuations in the house drain What is a vent stack? A vent stack prevents the development of excessive pressures in the lower regions of the drainage stack by relieving the air that is rapidly carried down the drainage stack. It does not include vertical fixture drains and branch vents that do not pass through more than two stories before being connected to the soil or waste stack or vent stack. What is a general term for any vertical line of soil or waste piping that collects water and wastes from fixture drains and horizontal branch drains from two or more floors of a building? A Stack. Properties of uniform flow apply to branches of what length and longer? 5 feet Special wastes, tank overflows, tank emptying lines, releif valve discharges, etc. should discharge where and why? Through an air break to an appropriate receptacle (floor drain or other) to prevent overpressurization of the drainage system. High temperature wastes should be cooled to what temperature before discharging into the drainage system? 140F When interior drainage piping developed length reaches 100 feet, what should happen and why? A vent to atmosphere should be provided. It should run independently through the roof, this is to prevent the rapid fouling of the pipe due to the growth of slime and fungi in the absence of air circulation. The sizing for indirect wastes is the same as direct-waste connections with what exception? Due to the low velocities usually present in indirect wastes, stoppages are more prevalent, and cleanouts should be provided at every possible location. For an indirect waste, the discharge outlet should be what? A minimum of 1.5 times the indirect pipe size above the flood level of the receptacle. How can the fixture unit flow rate be calculated? By dividing the total discharge flow in gallons per minute of a single fixture divided by 7.5 gal/ft^3 What factors do FUs account for? Application in conjunction with the probability of simultaneous use of fixtures. For interior drainage systems, the rate of flow in a fixture drain should be what? The same as the rate of flow discharged at the fixture outlet. For interior drainage systems, the minimum fixture drain size is what? The minimum size of the fixture trap (often given in a table) What is the recommended value of n, the coefficient of roughness, for storm drains of all sizes? 0.0145 The designer must know what as related to the sewer, water, and gas inverts and locations? The actual elevation of all of the floors of the building. What is the minimum velocity of flow to achieve scouring action in piping? For keeping grease in suspension in greasy wastes? For suspension in Storm Sewers? 2 fps, 4 fps, 3 fps. Dont forget to limit the length of runs for 1-1/2 and 2” pipe to maintain scouring action. What is the conversion for uniform flow velocity and capacity in sloping pipe going from from 1/4 in/ft slope to 1/8 in/ft? 1/2 in/ft? 0.707 and 1.414 The hydraulic mean depth of flow or hydraulic radius is what ratio and what value? The ratio of the cross sectional area of flow to the wetted perimeter of pipe surface, expressed as D/4 where D is diameter in feet. It is the same ratio for full and half flow. How is the quantity “rate of flow” expressed? Cross sectional area of flow times the average velocity. What formula determines the velocity of uniform flow in sloping drains? The Manning Formula Flow in piping and open channels is caused by what? The gravitational force induced by the slope of the drain and the height of water in that drain. How is maximum pressure drop calculated for a medical gas system? Identify the maximum pressure drop allowed for the specific gas system, divide it by equivalent length, and multiply by 100. In medical gas piping, how is diversity calculated? From simultaneous use factors given in a table. What are recommended minimum medical gas riser sizes? Oxygen: 3/4” Medical air: 3/4” Nitrous Oxide: 3/4” Nitrogen: 1” Vacuum: 1” What are minimum medical gas pipe sizes? Med gas mains and branches: 1/2” Vacuum mains and branches: 3/4” Drops to individual outlets/inlets: 1/2” Piping to alarm panels: 1/4” Where should medical gas piping be labeled? Every 20 feet, once in each room, at each side of every wall penetration, and at each floor level, and with the appropriate color. What joints are prohibited in medical gas systems? Flared or compression type, straight thread connections, clamp/gasket style couplings, pipe crimping tools, all joints that do not provide the mechanical, thermal, and sealing integrity of a brazed joint. What type of piping material is used for vacuum or WAGD medical gas? Seamless, hard-drawn type K, L or M copper tube or stainless steel tube. For level 3 vacuum systems, schedule 40 wall pvc plastic may be used. 0.2 to 0.5 in wc, never exceeding 10 percent of the available gas pressure. Describe the gas line coming into the building: It must have a minimum cover of 2 ft or greater, a curb valve should be installed at the tap off of the main, and a shutoff valve should be installed within 2 ft of the point of entry into the building. The point of entry into the building should be 10 feet away from any stairway. Before commencing design of the system, the engineer should contact the local utility company to determine what? Their rules and regulations, the point at which the utility company’s work ends and the contractors work begins, BTU value and pressure of gas supplied, any special requirements What is a special consideration for burying steel piping? Protect it with a corrosion-resistant material (bitumastic paint, etc.) What is the preferred material for gas piping, and when and what other materials can be used? Black steel is preferred, brass and copper can be used when the gas is not corrosive, stainless steel and corrugated stainless steel may also be used. Underground services 6” and larger can be cast iron, but it must be steel pipe entering the building. Don’t forget to use plug or ball valves rated for gas service. What special precautions must be used when designing LPG systems? LPG cylinders or appliances should not be located in pits, vaults, or basements unless they are mechanically vented. When they are located in a room, vents must be provided at floor level. Exterior locations may require proper separation of cylinders. With regards to natural and manufactured gas and LPG, what is their density compared to air? Natural and manufactured gas is lighter than air, LPG is heavier than air. How are propane and butane made available? They come in cylinders at a pressure of 80 to 120 psi. Pressure threshold is deemed “high pressure” for natural and manufactured gas? 2 psi. Low pressure gas is less than 2 psi, usually no greater than 0.5 psi (14 in wc). Gas is distributed throughout the building at 0.5 psi and on occasion, 1 psi. What is the name and heat content of the two types of LPG? Propane: 2,500 BTU/ft^3 and Butane: 3,175 BTU/ft^3 What is the heat content and water content of manufactured gas? 540 BTU/ft^3 and some water content, which may cause corrosion problems What is the heat and water content of natural gas? 1,000 BTU/ft^3 and a low water content What are the four basic types of fire and their symbols? A: Paper, Cloth, etc. [Triangle A] green B: Flammable liquid (gasoline, oil) [Square B] red C: Electrical [Circle C] blue D: Burning metals [Star D] yellow Name two types of flow alarms typically used in automatic sprinkler systems: 1) Vane Type / Pressure Type (the vane type is activated by a flow of water which sends an electrical signal to sound an alarm, the pressure type senses water pressure) 2) Water Motor (activated by the flow of water which turns a mechanical gong. this is a more positive method since it requires no electricity to operate) The jockey pump generally has a capacity of what? 2 to 5 percent of the fire pump capacity; it is set to start at about 10 psi above the pressure at which the fire pump is set to start. Under fire flow conditions, the jockey pump cannot keep up with the drop in pressure, triggering the fire pump to energize Where and why are jockey pumps used? With fire pumps, to maintain system pressure during non-operating conditions. What activates a fire pump? When the pressure in the fire sprinkler system drops below a set threshold which is typically the performance value of the jockey pump. To what is the fire pump supply and discharge connected to? The municipal or fire protection water supply at the intake and to the building’s sprinkler system risers at the discharge. (Fire pump installations are governed by NFPA 20) How is the overall fire demand established? By hydraulic calculations performed by the engineer, by code, or by the insurance rating organization The end result is the amount of flow required at a calculated pressure. What are the minimum pressure outlet requirements for hydraulically calculated standpipe systems? 100 psi (not to exceed 175 psi at the top) at the outlet of the hydraulically most remote 2-1/2” hose connection and 65 psi (not to exceed 100 psi at the top) at the outlet of the hydraulically most remote 1-1/2” hose connection. Ensure these values with a pressure regulating device or fire pump. What are the minimum flow rates for Class I and Class III standpipes? 500 gpm for the hydraulically most remote standpipe, 250 gpm per additional standpipe, with the total not exceeding 1250 gpm, or 1000 gpm for fully sprinklered buildings What is a Class III Standpipe? A system that provides trained personnel a 1-1/2” hose connection and a 2-1/2” hose connection for fire department/heavy fire stream trained personnel. What is a Class II Standpipe? A system that provides 1-1/2” hose connection to trained building personnel during an initial response. What is a Class I Standpipe? Provides a 2-1/2” hose connection for fire department and those trained in heavy fire streams Where is the need for standpipes outlined and what is their purpose? A check valve and shutoff valve (the shutoff valve on the discharge side of the check valve so the check valve can be serviced) What is a good rule of thumb for ejector vent sizing? Assign a size that is one-half the size of the subdrain discharge pipe into the basin, or a minimum of 3 inches. How many fixture units are equivalent to 1 gpm of pump discharge (in an ejector system)? 2 FUs When an ejector vent is connected to the building venting system, how is the addtional load on the vent pipe calculated? By converting the gpm discharge rate into FU. Ejector basins should not retain the waste discharge for a period exceeding how long? 12 hours In an ejector basin, the high and low water levels should be maintained where and why? The high water level should be at least 3 inches below the invert of the entering piping to prevent backflow and allow air circulation. The low water level should be at least 6 inches above the bottom of the basin to ensure the suction intake of the pump is covered by water. What is the minimum run time on an ejector system to avoid excessive pump cycling? 5 minutes of pump capacity between high and low water levels In an ejector system, how is the length of run measured and what its the minimum size? From the pump outlet to the highest point, it should be at least the same size as the pump discharge outlet. (after this point, the piping is sized as required for the gravity house drain) What is the recommended design velocity for flow in an ejector system? 5 - 10 fps. How do you determine the head of the ejector pump? Add the static head, measured from the low water line in the receiver up to the highest point pumped, and the friction head loss in the discharge piping and fittings. In a duplex sewage ejector system, each pump is sized to satisfy what condition? Peak inflow. What is used to size the ejector pump? Use the water supply fixture unit method to determine flow into the receiver, then total FU is converted to GPM using a table. When are pneumatic-type ejectors commonly used? When the discharge rate is 100 GPM or less, when large solids must be handled, where ground conditions are such that the space below the floor is restricted, where compressed air is readily available, and in explosion proof conditions. What two types of lifting devices are employed for the automatic discharge of sump or ejector basin contents? 1) Centrifugal pumps 2) Pneumatic ejectors A sump handles what? Clear waste water (sump basin not airtight, needs no venting) An ejector handles what? Sewage (ejector basin is airtight and requires venting) What is a subdrain? The portion of a drainage system that cannot drain by gravity into the building sewer. (these wastes flow into a receiving tank or sump, which is pumped into the gravity drainage system) On a pump curve, pump head (ft) is proportional to what? The ratio of the GPM squared The head in a typical system is comprised of what three components? (pump chapter) 1) Static head 2) Required pressure at each piece of equipment or fixture in the critical branch (total) 3) Friction head losses in the pipe and fittings (these vary with capacity) A centrifugal pump always operates at what condition? The intersection of its head/capacity curve and the system head/capacity curve. When selecting a centrifugal pump, in addition to determining the required head at the design capacity, it is very important to also check what? The system head/capacity curve to avoid possible future problems. The pump must be able of satisfying minimum and maximum requirements in addition to the design requirements. For parallel operation, the pump heads must be equal, but what may vary? Pump capacities. For series operation, the pump capacities must be equal, but what may have different values? Pump heads. For multiple pump system proper operation, all pumps should have what type of curve? Continuously rising characteristic. For parallel operation of two or more pumps, the combined performance curve is obtained by adding what? The capacities horizontally at the same heads. (100 GPM at 30‘ + 100 GPM at 30‘ = 200 GPM at 30’) For series operation of two or more pumps, the combined performance curve is obtained by adding what? The heads vertically at the same capacities. (100 GPM at 30‘ + 100 GPM at 30‘ = 100 GPM at 60’) When is a good time to use two or more pumps in parallel? When the system demand varies greatly. A curve where the head rises continuously as the capacity decreases, and is also called a rising head/capacity characteristic Vent terminals should be no smaller than what? The stack served (1-1/2 inches minimum). What is the minimum vent size to allow for frost enclosure? 3 inches What is usually an adequate size for sump or ejector vents? It has been found in practice that except for extremely large installations, 3 inches is usually an adequate size, but the vent should not be less than 1-1/4 inches. When designing sump or ejector vents, what requirements are applicable? All the requirements for the proper design of the sanitary system are applicable, thus, the air must be conveyed by the vent piping at the same rate as the maximum rate at which sewage enters or is pumped out of the receiver. What are some considerations when designing vapor vents? When a vapor vent is used, it must be isolated from the sanitary venting system and the stack must extend through the roof. The base of the vapor vent stack should terminate in a trap to prevent the escape of vapors and spill to a trapped, vented, and water-supplied receptacle. An individual vapor vent drip can be connected through an air gap to the inlet of the trap serving the fixture. The minimum stack size should be 13 inches, but should be sized by empirical methods or the rational approach. Where are vapor vents now applied? Sterilizing equipment and bedpan washers, and this is disappearing. These used to apply to water closets and urinals, but is no longer necessary. Where does the suds pressure zone extend to in a vent stack connected to a suds pressure zone? The suds pressure zone extends the vent stack base connection upward to the level of the suds pressure zone in the soil or waste stack. Where does the suds pressure zone extend to at the horizontal drain from the base of a stack? The suds pressure zone extends 10 stack diameters from the base fitting, and where an offset greater than 45 degrees in the horizontal occurs, the pressure zone extends 40 stack diameters upstream and 10 diameters downstream from the offset fitting. Where does the suds pressure zone extend to at the base of a soil or waste stack? The suds pressure zone extends 40 stack diameters upward from the base fitting. Where does the suds pressure zone extend to on an offset greater than 45 degrees? This zone extends 40 stack diameters upward and 10 stack diameters horizontally from the base fitting for the upper stack section. A pressure zone also exists 40 stack diameters upstream from the top fitting of the lower stack section. Name four areas where suds pressure zones exist: 1) At a soil or waste stack offset greater than 45 degrees 2) At the base of a soil or waste stack 3) At the horizontal drain from the base of a stack 4) In a vent stack connected to a suds pressure zone What design considerations must be taken into account where sudsing detergents are used? Whenever a soil or waste stack receives wastes from washing machines, dishwashers, laundry trays, kitchen sinks, etc., the drainage and vent piping for the lower floor fixtures or for the fixtures above offsets must be arranged to avoid connection to any zone where suds pressure exists. For equal rates of flow and pressure, how must vent pipe diameter for suds relief flow be sized compared to regular venting? The vent pipe diameter for suds pressure relief flow must be from 20 to 80 percent greater than for air flow. Are suds more or less dense than air? More dense, 2 to 19 lb/ft^3 depending on the detergent. Do vent pipe sizing tables generally account for the more demanding flow of suds? No. Where do high suds pressure zones occur? Every change in direction, either vertically or horizontally, that is greater than 45 degres. What happens with suds near the hydraulic jump or where relief paths are not available? Excessively high suds pressure can develop, blowing the seals off of the traps. How do air and water affect suds in a drainage stack? Air and water travel down the stack, the water passes through the suds without carrying them away, and air displaces the suds through any available outlet (drains, branches, vents, etc.) In sanitary drainage systems, where do suds occur? Suds flow down the stack and settle in the lower sections of the drainage system and at any offset greater than 45 degrees in the stack. Where should the relief vent connect? The lower end should connect to the drainage stack below the drainage branch connection, and the upper end should connect to the vent stack at least 3 feet above floor level. When should a relief vent be provided? In drainage stacks in buildings having more than 10 branch intervals at each tenth interval, counting from the topmost branch downward, or where a drainage stack offsets more than 45 degrees from the vertical. What do relief vents do? Balance constantly fluctuating pressures of multi story buildings by means of relief vents located at various intervals. Name some common rules for venting stack offsets. No drain connection can be within 10 feet of the bottom of the upper stack and not within 2 ft of the connection of the lower stack. The venting of the upper stack depends on the number of branch intervals above the offset. 60 inches, see table for other sizes. Name the four alternate methods acceptable in lieu of individual trap venting. Wet venting Stack venting Circuit and Loop Venting Combination waste and vent venting Can a vent terminal be extended through a wall? How? What should you consider for placement? Yes, but the terminal must turn down and be covered with a wire screen. It should never be located beneath a building overhang or immediately adjacent to an exterior building wall. Vent terminals should be how high above the roof level? 6 inches, unless the roof is used for other purposes, then it is at least 7 feet. Vent terminals should not be located near what? Unless what? Within 10 feet of any door, window, or ventilation intake unless they are extended at least 2ft above such openings. What is the size of the vent stack based on? What is it’s minimum size? The size is based on drainage fixture unit load and the developed length. It should be not less than one-half of the waste stack size. Where are the three places the vent stack can terminate? The vent stack should extend full size through the roof, connect to a vent header, or connect to the stack vent of the drainage stack at least 6” above the overflow of the highest fixture. Where is the most effective location for the vent stack? What is unique about this location? Below all drainage branch connections and preferable at the top of the horizontal drain immediately adjacent to the stack base fitting. This is the location where pressure is at it’s maximum and the danger of closure due to fouling is at its minimum. What is the purpose of installing a vent stack? To prevent the development of excessive pressures in the lower regions of the drainage stack by relieving the air as rapidly as it is carried down the drainage stack. How many branch intervals are permitted on a drainage stack for each attendant vent stack, according to the CPD manual? Two, and up to five in some codes. Can other things connect into the stack vent? The stack vent may be connected with the vent stack before extending through the roof or may be connected together with other stack vents or vent stacks in a vent header, and the vent header may be extended through the roof as a single pipe. Any connection to the vent stack is a _____? (various methods of fixture trap venting) Branch vent. Define Stack Vent The stack vent is the pipe from the topmost drainage branch connection through the roof to atmosphere. How is this circulation induced? The circulation is induced by the difference in head pressure between outdoor air and the air in the vent piping. This difference in head pressure is due to the difference in temperature and thus the difference in density of each air source and the height of the air column in the vent piping. The cool air, being more dense, displaces the less cool air and circulation is induced. The principle of gravity circulation of air is utilized to keep the entire sanitary system free of what? Foul odors, slime and fungi. What is the maximum length of vent piping for any particular size with a maximum allowable pressure drop of 1 in w.c.: the developed length or the equivalent length? What’s the difference? The equivalent length. At design conditions, how full is the drainage branch and what can be said about the air in the pipe? it is assumed that the drainage branch flows half-full at design conditions and that the air in the upper half of the pipe flows at the same velocity and capacity How are the rates of air discharge for a pressure relief vent stack sized? Through tables. Why is a vent stack provided in an area of high pressure (as water flows down the stack and enters the horizontal drain)? This is the area where hydraulic jump occurs. A vent stack is provided in this area of high pressure to provide an avenue for the flow of air to relieve the high pressure. Why must stacks be extended full size through the roof, and why may soil stacks not be reduced in size even though there is less load on the upper portions of the stack? As water falls down the stack, it exerts frictional drag on the core of air and as this air is dragged down, it must be replaced by an equivalent quantity of replacement air to avoid violent pressure fluctuations. At maximum design flow, water flows down the stack as a sheet of water occupying how much of the cross sectional area of the stack? 24-Jul When air flows in a pipe, a pressure loss occurs due to the friction between the air and the pipe wall. This loss of pressure is expressed by which formula? The Darcy Formula What pressure variations must be sustained at the 2” fixture trap for 100% safety factor? 1” W.C. How high is a column of air that is equivalent to the static pressure exerted by 1 in water column? 69.23 feet Design wise, what three things should one consider when placing a backflow prevention device? A pollutant is a nontoxic substance that does not represent an actual health hazard but impairs the water quality with respect to odor, taste, aesthetics, or other characteristics. What is the definition of a contaminant? A contaminant is a toxic substance that could affect the health and life of the consumer. What three basic factors determine the rate of circulation in hot water piping and the size of circulation piping to obtain that rate? 1. The heat loss rate of the piping 2. The temperature differential at which the system is to operate. 3. The allowable friction head loss in the piping. What effects do oversizing and undersizing have on a hot water circulating system? Oversizing will cause additional money to be spent on materials and create additional heat losses. Undersizing will seriously hamper circulation, thus preventing adequate hot water from being immediately available to all the fixtures. Since increased water temperatures can be damaging to pipes, what maximum hot water velocity should be used to keep the hot water from eroding the pipe? 6 fps for copper pipe, similar fps for other types of pipe. In lieu of a circulation system, what else can be done to maintain hot water temperatures in piping? Use heat trace. By what method does hot water supply piping (whether insulated or not) transfer heat to surrounding lower-temperature air? Convection, conduction, and radiation. Of the water stored in a storage hot water, what percentage is useable and why? 70 percent, because the stored water is cooled by the entering cold water. What is the primary reason for selecting a storage type water heater instead of instantaneous? To smooth out peak demands on heating systems with large-volume changes in hot water demand. When correct storage capacity is combined with the correct recovery capacity and the proper size of heating medium control valve, substantial reduction of the peak heating fluid demand can be realized. Name three advantages of a booster water heater. 1. Only as much water as is required for the specific job needs to be heated to above normal system temperatures. 2. Savings in capital costs, maintenance, and operating costs are derived from the limited use of very hot water. 3. Small boosters can be located near their jobs, with simple controls, minimal waste, and smooth operation. What is a booster water heater? A water heater that serves to raise the temperature of the regular hot water supply to some higher temperature needed to perform special functions. Describe a semi-instantaneous water heater (application, pros, etc.) A limited-storage type heater that contains between 10 to 20 seconds of domestic water storage according to its rated heating capacity. (A 60 gpm rated heater will have approximately 20 gal of water in its shell) This small quantity of water allows the temperature control system to react to sudden fluctuations in water flow and to maintain the outlet water temperature to within +/- 5 degrees F. What are the sizing of instantaneous hot water heaters most commonly based on? Fixture units. Peak demand for hot water using this method is two to three times actual demand, so it is recommended that usage factors be applied to select the most economically sized instantaneous hot water heater. Name one problem with instantaneous water heaters. Adequate control of the temperature of the outlet water to within acceptable limits during fluctuating demand. This fluctuation is called overshooting or undershooting. The heat transfer rate increases or decreases when water velocity increases in the tubes? increases. What is the minimum velocity that should be maintained through the tubes on an instantaneous water heater? 4 fps. This will minimize the rate of scale formation in the tubes. How should the instantaneous water heater be configured if the characteristics of water are such that rapid scale deposits are possible? A straight-tube, floating head exchanger should be used in lieu of the U-tube heater. What is the most common form of instantaneous water heater? The U-tube, removable bundle exchanger with steam or boiler water in the shell and domestic water flowing through the tubes. What should always be provided with instantaneous water heaters? A hot water temperature limit to prevent scalding water from entering the system. This is becoming more standard regardless of the type of water heater used. Describe Instantaneous Water Heaters (application, pros, etc.) No built in storage, designed to deliver full capacity rapidly and continuously. Must have sufficient capacity to meet all demands simultaneously. Require a high heat input to meet the required discharge rate and temperature of hot water. Best applied where demands are level and constant, such as swimming pools, dishwasher boosters, industrial processes. They heat the water through conduction. When using a fuel fired water heater, you must always provide what? Combustion air Describe Direct Fired Storage water heaters (application, pros, etc.) Simple, inexpensive in installation, piping, controls. Used in homes, small commercial. Low demand heaters with low btu inputs so the heating of the water is spread over several hours. What is a good standard hot water temperature and why? 140F because it kills legionella and other harmful bacteria Exclusively on the basis of total pressure available for friction head loss and the longest equivalent length of run (ELR). Which formula are most all friction head loss tables and charts based on? The Darcy-Weisbach formula. Describe the procedure for sizing domestic water systems: Step one: Draw a riser diagram of the complete water distribution system showing floor to floor heights, the static pressure at each floor, the minimum pressure required at the highest outlet and the minimum available pressure. Step two: Mark the FU value at each outlet and the sum of FUs for every section of the system. (Add FU values, not GPM values, except for continuous demands). Step three: Convert all FU values to GPM values and assign GPM to continuous demand outlets. Step four: Determine the pressure available for friction head loss and establish the uniform friction head loss. Remember the furthest fixture may not always be the controlling fixture. Step five: Use hydraulic tables or charts to select sizes. The selection will be based on gpm demand, uniform friction head loss, and max design velocity. Remember to make sure the size selected doesn’t exceed the maximum allowable velocity. Why are minimum pipe sizes given in domestic water design? To maintain the velocity of the flow below the maximum 10 fps. In parallel circuits, the _____ in each branch is such that the _____ _____ is also equal. Flow, pressure drop. What is the maximum friction head loss that can be tolerated in the system during peak demand? The difference between the pressure at the outlet of the meter minus the flow pressure required at the fixture minus the pressure drop of any equipment or piping accessories in between. Why must friction head losses be limited in the water piping system? So that the highest and most remote water outlet will have the required minimum pressure for adequate flow during periods of peak demand. The water distribution system must always be designed on the basis of ____? The minimum pressure available. How do you estimate the demand for a system with both continuous and intermittent fixtures? Estimate the continuous demand separately from the intermittent demand and add this amount in gpm to the demand of the fixtures in gpm. What was the name of the standard that first introduced fixture unit tables? BMS 65, Methods of Estimating Loads in Plumbing Systems by Dr. Roy B Hunter (published in the 1940s by the National Bureau of Standards). What factors are “fixture units” based on? Weighting fixtures in accordance with their water supply load-producing effects on the water system. Name and describe the two methods of determining peak demand for domestic water systems in the US. Empirical method and Method of Probability. EM: Based on arbitrary decisions arrived at from experience and judgement and is useful for only small groups of fixtures. MP: Based upon the theory of probabilities and is most accurate for large groups of fixtures. (Never use for a small number of fixtures.) Remember to add FU values and not GPM values. Add all FUs first, then convert to GPM. Give examples of continuous demand outlets and intermittent demand outlets. Continuous: hose bibbs, lawn irrigation, air-conditioning make up, water cooling, etc. Intermittent: plumbing fixtures. Define Maximum Flow, Average Flow, and Maximum Probable Flow: The flow that will occur if the outlets on all of the fixtures are opened simultaneously (maximum possible flow). The flow that is likely to occur in the piping under normal conditions. The maximum flow that will occur in the piping under peak conditions (peak demand or peak flow). What is an easy way to eliminate noise problems in plumbing? Maintain a flow velocity under 8 FPS in all parts of the pipe. Describe the phenomenon of cavitation. The centrifugal force developed around a short bend radius at high velocity causes an increase of pressure at the outer bend with a resultant lowering of pressure at the throat. This low-pressure zone can drop below atmospheric pressure to a pressure that corresponds to the boiling point of the flowing fluid. Under this condition, the cavity that forms at the inside of the bend permits the fluid to flash into vapor or steam bubbles. Once these bubbles flow past the low-pressure zone into normal pressure area downstream, these bubbles collapse. As the bubbles collapse, they literally tear the metal off the pump casing, causing a pitted facia. What can cause cavitation to occur in piping? When the direction of flow is sharply changed and the velocity of flow is high, fluids flowing around a short bend radius at a high velocity. The pressure loss of flowing fluid due to friction varies approximately with the square of _______, and is directly related to _________? The Velocity, the roughness of the pipe wall. What kind of valve should always be installed in the discharge line of pumps and why? Spring-loaded check valves because they are designed to close at the exact moment water flow comes to a rest. The velocity of flow does not change when the check closes, thus no hydraulic shock is produced. What kind of valves should never be used in the discharge line of pumps and why? Swing check valves, because when the pump stops, a reversal of flow occurs, and the check slams closed, causing a sudden change in velocity. What is one device that was used as a means of controlling hydraulic shock until it was deemed ineffective? Air chambers. They often were improperly sized and almost always lost their air charge. What is a simplified expression for the increase in pressure caused by hydraulic shock? The Jacowsky Formula What are the most common causes of hydraulic shock? How do you convert from psi to feet of head? Multiply psi by 2.31. How do you convert from feet of head to psi? Multiply the height by 0.433. What is static head and where does it occur? Static head is a measure of potential energy of a fluid and it occurs whenever a free surface of water is exposed to atmospheric pressure. In turbulent flow, which has the largest effect on flow? (Pipe roughness or velocity?) Roughness significant, velocity negligible. In laminar flow, which has the largest effect on flow? (Pipe roughness or velocity?) Viscosity significant, roughness negligible. What is the Reynolds Number for critical velocity in a domestic water system? 2,100 What is the Reynolds Number Range of critical velocity in a pipe? 2,000 to 4,000 What is critical velocity in a pipe? The turning point between laminar (streamline, viscous) flow and turbulent flow. What is the main point behind supports, anchors, loops, guides and expansion joints? To control piping expansion occurring with any change in temperature and cause it to move in the direction desired by the designer. If expansion in a branch is not adequately accounted for, the branch may break causing flooding damage. Does the bellows type joint satisfy the design limitation for movement? What is the limitation and are guides required for a bellows joint? The Bellows joint is very satisfactory for the 1-1/2 inch design limitation on movement. Guides should be used with this type of joint to prevent an offset movement. Describe some design considerations of a slip type joint. The slip type joint requires packing and lubrication, and therefore maintenance access. Guides must also be installed in the lines into the slip joint to keep the pipe from bending and binding in the joint. What are two types of thermal expansion joints? The slip type and the bellows type. How is movement accommodated in expansion fittings? By the flexure of the pipe (never by a rotating motion of the fittings). The developed length of pipe available for flexure is the only thing that limits the amount of expansion that can be accommodated. The number of elbows does not matter. What is one of the most persistent myths in plumbing related to thermal expansion? Turning motion occurs at the elbows of an expansion loop. This is absolutely false. Would you say that expansion joints are required in the great majority of piping systems? No, the expansion loop or joint is usually omitted in most piping systems by taking advantage of the changes in direction normally required in the layout. What is the maximum total movement that should be absorbed by any expansion loop or offset? 1-1/2 inches. What two methods are usually employed to absorb pipe expansion or contraction without danger to the piping? "1. Expansion loops and offsets 2. Expansion joints" When piping cannot move freely, where does failure due to thermal expansion and contraction usually occur? At the pipe joints and fittings, as the pipe itself can usually withstand these stresses. If piping is restrained from moving, it will be subjected to what kind of stresses? Compressive stress on a temperature rise, and tensile stress on a temperature drop. Define “Coefficient of Expansion” The unit increase in length of a material per 1 degree F increase in temperature What type of pipe is not acceptable for storm sewers and why? Vitrified tile pipe because it is brittle and weak in larger diameters. What are typical pipe types used for different areas of storm sewers? For building connections Between the building sewer and the first downstream structure, cast iron soil pipe is recommended. This pipe will better withstand shock loads from materials and equipment likely to be encountered within close vicinity of buildings, and has a large variety of fittings available. Reinforced concrete pipe is most satisfactory for general use elsewhere, and is often not readily available in sizes under 12 inches. PVC may also be used. Check the code. Name three types of drainage structures (for site drainage) Manholes: used where no surface water enters the system Drain inlets: used in any point in paved areas where surface water enters the sewers Catch basins: which are similar to drain inlets but are located in grassy or unimproved areas. When designing site drainage, how is the equivalent area calculated? The equivalent drainage area of each inlet and building connection is taken into account. The equivalent area is the product of the actual area in acres times the runoff coefficient, C. The runoff coefficient is based on the absorption capabilities and the surface roughness characteristics of the surface across which the water will drain. What are the four rules for hydraulic design, ensuring the establishment of the exact size, slope, and invert of all sewer pipes? "1. Slopes should provide a minimum velocity of 2.5 fps under design conditions to prevent deposition within the pipe during periods of peak flow. 2. Cover over piping will vary. Verify structural ability of the piping material to carry loads. 3. Sufficient change in pipe invert should be The perforations should be pointed downward, and should be surrounded by a minimum of 12” pea gravel, number 1 stone, or number 2 stone. What should sub-soil drains be made of? Open-jointed, horizontally split or perforated clay tile, perforated bituminized-fiber pipe; or plastic pipe, not less than 4” in diameter. Where do subsoil drains typically go? Under the lower-level or basement floor, or around the perimeter of the building. What minimum velocity is required for storm water piping? And what is the minimum for sanitary piping? 3 fps and 2 fps. Special pipe sizing applies to which type of roof drains and why? Siphonic roof drains, which restrict the air flow and swirl, allowing full use of the downspout for water only. Where should strainers be used and how big should the open area be? Mushroom, or domed, strainers should be used for roofs where leaves or other debris may accumulate. Corner strainers are required when the drain is located at the corner of the roof and the parapet or a vertical wall. The open area of the strainer should be 1.5 to 2 times the area of the pipe to which it connects. Name the three basic components of a roof drain: Strainer, flashing ring (and gravel stop, where required) and drain body or sump. Are vertical walls included in the calculation for stormwater runoff? Some codes require 50 percent of the area of vertical walls be added to the horizontal drained area. Some do not. At 4 in/hr rainfall, roughly how much area will result in 1 gpm of rainfall? 24 sq.ft To apply this for other rates of rainfall, multiply (24x4) and divide by the new rate. (There should be tables for this in all plumbing codes) What is the design criterion for storm water sizing? The required rate of discharge from any collection area, dependent on the size of the area, and the maximum rate of rainfall per hour. Why is condensation a concern for roof drainage and how can it be overcome? Low temperature liquid flow in storm water piping will cause condensation to form on piping inside the building. Insulation of pipes and roof drain bodies will keep the condensation from dripping onto the ceiling or floor. The connection to roof drains should always use what? An expansion joint, either integral or separate. This prevents the pipe expansion and contraction (from severe outdoor temperature swings and a fairly constant inside temperature) from raising the roof drain and destroying the integrity of the water proofing at the roof. If the storm piping is run separately from the sanitary piping, how many traps are required before connection to the sanitary system or combined sewer? One. What is different about storm water drainage system design? Design of a storm drainage system is based on the piping flowing full under uniform flow conditions. Downspouts (also called conductors or leaders) and horizontal piping can also flow full as maintaining hydraulic pressures within any fixed limits in the system is not necessary as it is in a sanitary drainage system. Define Stormwater: Rainwater, surface runoff, ground water, subsurface water, or similar clear liquid wastes, exclusive of sewage, condensate, and industrial waste What does the Manning Formula describe? The velocity of uniform flow in sloping drains.