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ASPE CPD Study Questions AH with
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Front - correct answer. Back
What is the specific weight of water? - correct answer. 62.4 lbs per cubic foot
What happens in a storm and sanitary system after it passes the water test? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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
How many fixture units are equivalent to 1 gpm continuous or semicontinuous flow and what are examples of these types of flow? - correct answer. 2 FUs, sump pumps, ejectors, air conditioning equipment, water cooled, equipment, etc
What minimum slopes are required for building drains and why? - correct answer. 3 in pipe and smaller: 1/4 in/ft 4-6 in pipe: 1/8 in/ft 8 in pipe and larger: 1/16 in/ft to maintain 2 fps scouring action if low flow fixtures are present, 1/4 in/ft for all is a good idea
House drains are designed to flow how full? - correct answer. 1/2 full to 3/4 full max under uniform flow conditions
What is a house (building) drain? - correct answer. The lowest piping of a gravity drainage system that receives the discharge from soil, waste, and other drainage pipes inside the building that extends a short distance from the building and conveys the drainage to the building sewer
(vertical or horizontal position). (The tee-wye is also called a combination wye and one- eighth bend)
What is the difference between soil stacks and waste stacks? - correct answer. Soil stacks collect wastes that contain fecal matter, and waste stacks collect wastes that do not contain fecal matter (lavatories, sinks, etc)
What is a vent stack? - correct answer. 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? - correct answer. A Stack.
Properties of uniform flow apply to branches of what length and longer? - correct answer. 5 feet
Special wastes, tank overflows, tank emptying lines, releif valve discharges, etc. should discharge where and why? - correct answer. 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? - correct answer. 140F
When interior drainage piping developed length reaches 100 feet, what should happen and why? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. By dividing the total discharge flow in gallons per minute of a single fixture divided by 7.5 gal/ft^
What factors do FUs account for? - correct answer. 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? - correct answer. The same as the rate of flow discharged at the fixture outlet.
For interior drainage systems, the minimum fixture drain size is what? - correct answer. 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? - correct answer. 0.
The designer must know what as related to the sewer, water, and gas inverts and locations? - correct answer. 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? - correct answer. 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? - correct answer. 0.707 and 1.
The hydraulic mean depth of flow or hydraulic radius is what ratio and what value? - correct answer. 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? - correct answer. Cross sectional area of flow times the average velocity.
What formula determines the velocity of uniform flow in sloping drains? - correct answer. The Manning Formula
Flow in piping and open channels is caused by what? - correct answer. 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? - correct answer. 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? - correct answer. From simultaneous use factors given in a table.
What are recommended minimum medical gas riser sizes? - correct answer. Oxygen: 3/4” Medical air: 3/4” Nitrous Oxide: 3/4” Nitrogen: 1” Vacuum: 1”
What is a WAGD system? - correct answer. Waste anaesthetic gas disposal system includes oil-les/inert vacuum producers, and is required at each anesthetizing location. It is violet colored and gas specific. The minimum flow/Hg is determined by patient equipment requirements
What are the three levels and their ramifications in terms of potential patient risk if a medical gas system fails? - correct answer. Level 1: Places patients in imminent danger of morbidity or mortality Level 2: Places patients at manageable risk for morbidity or mortality Level 3: Terminates procedures but would not place patients at risk of morbidity or mortality
What is the definition of medical gases and can you name the 8 major gases? - correct answer. Gases that are used as part of a healthcare procedure other than for normal body functions. 1) Oxygen, 2) Medical Air 3) Nitrous Oxide 4) Carbon dioxide 5) Nitrogen 6) Instrument Air 7) Vacuum and 8) WAGD
What two methods of gas sizing may be used? - correct answer. 1) The longest length method sizes the main from the meter to the farthest gas user (stay constant along the maximum horizontal length). The same maximum length can be used for branches. 2) The branch length method sizes the branches (not the main) based on their individual actual lengths from the meter.
What five factors are involved in the sizing of gas systems? - correct answer. 1) Allowable pressure drop from meter to farthest outlet 2) Demand (load) in (ft^3/h) 3) Actual length of run (see NFPA 54 National Fuel Gas Code for gas sizing tables) 4) Specific gravity of gas 5) Diversity factor (or factor of usage) if allowed by code
What is the testing procedure for the gas piping? - correct answer. The entire system should be subjected to an air test for 10 min at a pressure that is twice the working pressure without showing any loss of pressure.
What design considerations are there for gas piping within a building? - correct answer. All risers should be valved, and drips should be located at all low points in the building and at the base of all risers. Connections from the mains should be from the top or side whenever possible, if impossible, a connection can me made from the bottom with either a drip or a pitch down to the main in the branch piping. Each piece of equipment should have a shutoff valve.
What range should the total pressure drop fall within from the gas meter to the farthest outlet? - correct answer. 0.2 to 0.5 in wc, never exceeding 10 percent of the available gas pressure.
Describe the gas line coming into the building: - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. Natural and manufactured gas is lighter than air, LPG is heavier than air.
How are propane and butane made available? - correct answer. They come in cylinders at a pressure of 80 to 120 psi.
Pressure threshold is deemed “high pressure” for natural and manufactured gas? - correct answer. 2 psi. Low pressure gas is less than 2 psi, usually no greater than 0. 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? - correct answer. Propane: 2,500 BTU/ft^3 and Butane: 3,175 BTU/ft^
What is the heat content and water content of manufactured gas? - correct answer. 540 BTU/ft^3 and some water content, which may cause corrosion problems
What is the heat and water content of natural gas? - correct answer. 1,000 BTU/ft^ and a low water content
What are the four basic types of fire and their symbols? - correct answer. 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
Where is the need for standpipes outlined and what is their purpose? - correct answer. The adopted building and/or fire code. The purpose of installing a standpipe system is to give fire department personnel a readily accessible water supply during fire events. They may either be wet or dry type.
What approach are most fire sprinkler designs based on? - correct answer. Area and density approach. Water flow requirements are based on degree of hazard, the design area is a theoretical worst-case scenario, and the design density is a measurement of how much water per square foot of floor area should be applied to the design area.
What are the four common types of automatic water-based sprinkler systems? - correct answer. 1) Wet pipe 2) Dry pipe 3) Deluge 4) Preaction
What are the four authorities that may have jurisdiction regarding fire sprinkler design? - correct answer. 1) State fire marshal 2) Local fire department 3) Building department 4) Insuring agency
What does NFPA 24 address? - correct answer. Standard for the Installation of Private Fire Service Mains and Their Appurtenances
What does NFPA 20 address? - correct answer. Standard for the Installation of Stationary Pumps for Fire Protection
What does NFPA 14 address? - correct answer. Standard for the installation of Standpipe and Hose Systems
What does NFPA 13 address? - correct answer. Standard for the Installation of Sprinkler Systems (13D: one and two family dwellings) (13R: residences up to and including 4 stories)
Design information for automatic sprinkler systems in non-residential properties is set by who? Are these mandatory provisions? - correct answer. NFPA, just recommendations unless referenced in other codes.
What plays a role in determining whether or not fire sprinklers are required? - correct answer. Building height and use classification.
How does a fire suppression system work against the “fire triangle”? - correct answer. Fire suppression systems put out fires by taking away one or more elements from the fire triangle
What three things make up the “fire triangle”? - correct answer. Oxygen, heat, and fuel.
What pump capacity is thought of as “good design” for sump basins? - correct answer. 1-1/4 times the maximum inflow to protect against unusual flow conditions, and
a duplex sump system (each sized at 1-1/4 the max inflow) should be used for rainfall collection to protect against flooding in the event of pump failure during a storm. Also, a source of emergency power for storm water sump pumps is a good idea because storms and power failures often occur at the same time. (you may use a VFD with a sump pump)
For paved and impervious areas collected in a sump, how is runoff calculated? - correct answer. A value of 1 gpm for every 24 sf can be assigned for locations where the annual rate of rainfall is 4in/hr
How is the rate of discharge from a subsoil drainage system calculated? - correct answer. By assigning a value of 2 gpm for each 100sf area where the soil is sandy and 1 gpm per 100sf for clay soils. Don’t forget to add the additional flow rate of clear water wastes such as condensate drains, etc.
What should always be provided to keep harmful debris away from the pump in a sump basin? - correct answer. A settling basin.
What kind of check valve should be used for pump discharge lines from sump/ejector basins and why? - correct answer. A spring-loaded or weight-loaded check valve, to keep the water from running back into a discharge basin and short cycling the pump.
What should always be installed at the discharge of each pump discharge line (sump/ejector basin)? - correct answer. 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? - correct answer. 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)? - correct answer. 2 FUs
When an ejector vent is connected to the building venting system, how is the addtional load on the vent pipe calculated? - correct answer. By converting the gpm discharge rate into FU.
Ejector basins should not retain the waste discharge for a period exceeding how long? - correct answer. 12 hours
In an ejector basin, the high and low water levels should be maintained where and why?
- correct answer. 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.
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? - correct answer. 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? - correct answer. 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? - correct answer. Pump capacities.
For series operation, the pump capacities must be equal, but what may have different values? - correct answer. Pump heads.
For multiple pump system proper operation, all pumps should have what type of curve?
- correct answer. Continuously rising characteristic.
For parallel operation of two or more pumps, the combined performance curve is obtained by adding what? - correct answer. 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? - correct answer. 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? - correct answer. When the system demand varies greatly.
What is the benefit of operating pumps in parallel? - correct answer. To obtain greater capacities.
What is the benefit of operating pumps in series? - correct answer. When it is not advantageous or efficient to add additional stages to a single pump, pumps are operated in series to obtain greater heads.
What does NPSHr vary with? - correct answer. The speed and capacity of the pump.
Define “vapor pressure” - correct answer. The pressure a liquid exert on its surroundings (this varies directly with temperature)
When calculating NPSH, use which pressure, absolute or gauge? - correct answer. Absolute. To convert psi (or psig) to feet absolute, add the barometric pressure (14.7 psi
at sea level) to the liquid psi to obtain psia, and then multiply by 2.31 to obtain feet absolute.
How does one avoid pump cavitation? - correct answer. Ensure the NPSHa (available, determined by system) is greater than the NPSHr (required, a function of the pump).
What are some adverse effects of pump cavitation? - correct answer. In addition to impeller damage, cavitation generally results in reduced pump capacity (due to presence of vapor in the pump), the pump head may also be reduced and exhibit some instability, the power consumption may become erratic, and vibration and mechanical damage such as early bearing failure can also occur.
What are the definitions of each of the pump affinity laws in terms of IMPELLER DIAMETER? - correct answer. 1) The capacity varies with the diameter 2) The head varies with the square of the diameter 3) The brake horsepower varies with the cube of the diameter
When altering a pump impeller, what percent decrease can be achieved without adverse effects? - correct answer. For an average impeller, 20 percent of the original maximum diameter.
What are the definitions of each of the pump affinity laws? - correct answer. 1) The capacity for a given point on the pump head/capacity curve varies with the speed 2) The head varies with the square of the speed 3) The brake horsepower varies with the cube of the speed
Why are pumps with non-overloading power curves advantageous? - correct answer. The drive is not overloaded under any operating condition.
What is the telltale sign of an overloading BHP pump curve? - correct answer. When the BHP curve continues to increase with increased capacity
What does a non-overloading pump BHP curve look like? - correct answer. A curve that flattens out and decreases as the capacity increases beyond the maximum efficiency point.
For a pump, describe “flat characteristic curve” - correct answer. This is a curve where only a slight variation in head occurs from shutoff to design capacity. The curve might also be drooping or rising (it will still have a portion where the head is approximately constant over a range of capacity, called the flat portion). This curve is NOT desirable for putting pumps in parallel.
For a pump, describe “steep characteristic curve” - correct answer. This is a rising head/capacity characteristic curve where a large increase in head is developed at shutoff in relation to the head developed at design capacity. This curve is ideal for putting pumps in parallel.
Where does the suds pressure zone extend to at the base of a soil or waste stack? - correct answer. 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? - correct answer. 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: - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. More dense, 2 to 19 lb/ft^ depending on the detergent.
Do vent pipe sizing tables generally account for the more demanding flow of suds? - correct answer. No.
Where do high suds pressure zones occur? - correct answer. 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? - correct answer. Excessively high suds pressure can develop, blowing the seals off of the traps.
How do air and water affect suds in a drainage stack? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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. - correct answer. 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.
With respect to the horizontal axis, what degree can an offset be and still be considered horizontal? - correct answer. Less than 45 degrees. Any offset 45 degrees and greater is considered a horizontal offset and sized as such.
What is another name for “island venting”? - correct answer. Loop venting.
Describe “combination drain and vent” - correct answer. This serves a drain line that has horizontal branches, and no food waste grinders or chemical sinks can be included. This pipe carries air and water, and in some codes, the permitted sizes are one size more than the calculated drain size. (Other codes use a table).
Describe “circuit vent” - correct answer. A circuit vent may be used for a maximum of 8 fixtures. All fixtures must connect horizontally to the horizontal branch drain being circuit vented, and the connection shall be between the two most upstream fixture drains. It shall be a dry vent sized for all DFUs of the drain. If there are four or more water closets, provide a relief vent, which shall be the same size as the circuit vent and may be a wet vent. This drain line of the circuit vent must be full size for the entire length of run.
Describe “waste stack vent” - correct answer. The waste stack in this case acts as the waste stack and vent. No offsets, water closets or urinals are included, each fixture connects separately, and fixtures must be of the same type. Some codes limit this arrangement to three floors. This has special sizing tables and the stack shall be the same size for its entire length.
Describe “horizontal wet venting” - correct answer. This method is used for bathroom groups of fixtures in one or two bathrooms where the fixture drains are in a row and not one above the other. This common vent and waste pipe will be larger, so look for a special table. In some cases a relief vent will be required.
Vent terminals should not be located near what? Unless what? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. Two, and up to five in some codes.
Can other things connect into the stack vent? - correct answer. 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) - correct answer. Branch vent.
Define Stack Vent - correct answer. The stack vent is the pipe from the topmost drainage branch connection through the roof to atmosphere.
How is this circulation induced? - correct answer. 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? - correct answer. 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? - correct answer. The equivalent length.
At design conditions, how full is the drainage branch and what can be said about the air in the pipe? - correct answer. 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? - correct answer. 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)? - correct answer. 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? - correct answer. 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? - correct answer. 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? - correct answer. The Darcy Formula
What pressure variations must be sustained at the 2” fixture trap for 100% safety factor? - correct answer. 1” W.C.
How high is a column of air that is equivalent to the static pressure exerted by 1 in water column? - correct answer. 69.23 feet
Design wise, what three things should one consider when placing a backflow prevention device? - correct answer. 1. all backflow prevention devices have a high pressure drop that the design must compensate. 2. good plumbing design is to add a strainer upstream of the backflow device to prevent debris from obstructing the check valves 3. if using a reduced-pressure backflow device, these have a high relief discharge rate, which must be accommodated
