Pumped Network with Pipes Lower than Source Tank
Pumped Network with Pipes Lower than Source Tank
(OP)
Dear All,
I have searched this forums but couldn't find a thread that describes what am facing exactly so I started this one.
I have a pressurized piping network that is being fed from a pump station and a reservoir that is higher than most of the pipes of the network (the pumps are required in order to deliver extra pressure at withdrawal points and to overcome friction).
When the pumps are not in operation, there is a possibility of having the source tank drain by gravity through the faucets as it is higher than most withdrawal points.
In order to prevent that, I have suggested to force a gooseneck at the pump station just downstream the pumps check valve and the hydropeumatic tank. This is by raising the discharge pipe to a level of 50cm higher than the water level in the tank and place an air valve (vaccuum breaker) at the high point before going down again to the original level and connect to the network.
When power is turned off, flow from the tank (without the pumps in operation) will create a syphon which shall be broken by the vacuum breaker valve and stop the flow.
Is this solution feasible? Is there another alternative?
What precautions shall I consider while designing surge protection for the network (against power failure)?
For power failure, I have placed a typical hydropneumatic tank just downstream the pumps (a bypass line will not work efficicently as the source tank is not much higher than the pump). The problem is that the hydropneumatic tank shall drain completely to the network after power failure. Is using bladder type surge tank more suitable in that case? Also, negative pressures form in the network at high points when the pipes tend to drain by gravity through faucets located at the low points. If I place vacuum breaker valves at thse high points I shall facilitate draining of the network after power failure; Is this acceptable?
Any help will be much appreciated, this is the first time to deal with such situation.
Thanks in Advance
Mohamed Elkordy, M.Sc.
I have searched this forums but couldn't find a thread that describes what am facing exactly so I started this one.
I have a pressurized piping network that is being fed from a pump station and a reservoir that is higher than most of the pipes of the network (the pumps are required in order to deliver extra pressure at withdrawal points and to overcome friction).
When the pumps are not in operation, there is a possibility of having the source tank drain by gravity through the faucets as it is higher than most withdrawal points.
In order to prevent that, I have suggested to force a gooseneck at the pump station just downstream the pumps check valve and the hydropeumatic tank. This is by raising the discharge pipe to a level of 50cm higher than the water level in the tank and place an air valve (vaccuum breaker) at the high point before going down again to the original level and connect to the network.
When power is turned off, flow from the tank (without the pumps in operation) will create a syphon which shall be broken by the vacuum breaker valve and stop the flow.
Is this solution feasible? Is there another alternative?
What precautions shall I consider while designing surge protection for the network (against power failure)?
For power failure, I have placed a typical hydropneumatic tank just downstream the pumps (a bypass line will not work efficicently as the source tank is not much higher than the pump). The problem is that the hydropneumatic tank shall drain completely to the network after power failure. Is using bladder type surge tank more suitable in that case? Also, negative pressures form in the network at high points when the pipes tend to drain by gravity through faucets located at the low points. If I place vacuum breaker valves at thse high points I shall facilitate draining of the network after power failure; Is this acceptable?
Any help will be much appreciated, this is the first time to deal with such situation.
Thanks in Advance
Mohamed Elkordy, M.Sc.





RE: Pumped Network with Pipes Lower than Source Tank
Have you considered the installation of an energize to open fail close valve in the suction line to the pump? One would think it unwise to rely on the gooseneck as you would have to carefully design the pressure conditions under which it would work. The pressure conditions consist of very low head and velocity head and will be difficult to make work at such conditions of low pressure.
You should have an emergency generator for the power failure scenario such that you have a minumum water distribution system pressure of 20 psig at all times. It is not good practice to use vacuum breakers as you will be required to disinfect after losing pressure in the water distribution system.
RE: Pumped Network with Pipes Lower than Source Tank
Thank you for your response,
What do you mean by "an energize to open fail close valve in the suction line to the pump"?
I think I will have air into the system any way when I loose pressure (when power fails) as there are high points in the network with air valves installed. they shall help draining the lines to the faucets.. I know that this should be an emergency situation but I am afraid of loosing all the water of the hydropneumatic tank as well.. that's why i need to install something to shut the flow down when power fails. This will prevent the source tanks from draining, prevent the hydropneumatic tank from draininf completely, and also prevent having water flow through the vanes of the pumps when they are not in operation..
what do you think?
RE: Pumped Network with Pipes Lower than Source Tank
RE: Pumped Network with Pipes Lower than Source Tank
Is it manual or auto?
If water is continue being drawn from the system while the pump is off, you may face a situation where the pump is started with an empty pipe line that is -ve static head. If the flow velocity is high you will face a water hammer situation. You will need to size the air vent valve correctly to avoid too fast filling.
Anther scenario is the air vent valve will not work if the goose neck has full flow during pump starting.
You did not gave detail of the pump flow rate and pressure and also the piping system. If the flow velocity is low, surge will not be an issue.
RE: Pumped Network with Pipes Lower than Source Tank
Operation at the pump station is automatic.. I have 6 pumps operating in parallel during period of high demand (total flow of 330 lit/sec and velocity 1.6m/sec) and this number decreases with demand decrease according to the pressure.. when no flow is being withdrawn, the network should be kept pressurized...
The situation of loosing pressure at the pump station is an emergency situation when power fails at the station (during period of high demand which is more critical).. In this case, water still flows through the faucets and the network could drain completely. I thought of the gooseneck with air valve to prevent the source tank from draining too...
We shall put precautions on startup of the station when power is back to fill in the lines slowly.. However I don't know how can this be done (the pressure is now almost zero at the pumps and all 6 pumps should be triggered to operate once power is back)..
RE: Pumped Network with Pipes Lower than Source Tank
RE: Pumped Network with Pipes Lower than Source Tank
RE: Pumped Network with Pipes Lower than Source Tank
The air release valve can be sized to allow a controlled venting of the air based on the pump capacity and empty pump volume. Reputable valve manufacturer will have their own sizing method based on their valve design.
The air valve also helps to prevent water hammer in the event of power failure by admitting air into the system.
RE: Pumped Network with Pipes Lower than Source Tank
RE: Pumped Network with Pipes Lower than Source Tank
You may be comforted, but an air release valve will simply not work properly at the near atmospheric pressures that you will encounter. There will not be adequate head to close the air release valve. Air release valves are not designed to operate at 1-2 psig (approximately atmospheric head).
The air release will definitely cause water hammer because it will allow a phase separation to occur when air is introduced into the pump and pipeline. The introduced air will also defnitely destroy the pump(s).
I fail to understand why any responsible person would ever want to introduce air into a centrifugal pump. That will destroy a centrifugal pump quickly! Here is a reference:
"An air locked pump will overheat in a matter of minutes."
Refer to page 8-18 of this document:
http://
This application is also way too large to use a hydropneumatic tank. Hydropneumatic tanks are normally used on applications with flows of 3 l/sec not 330 l/sec.
All automatically operated valves come with solenoid venting control devices that allows the valve closure time to be adjusted. Here is an example of inexpensive devices that allow slow closing of valves:
ht
Probably the least expensive method is to get a check valve that includes the automatic closing option. See the link below:
http://www.controlvalves.com/series/94/94.html
The Series 94 is designed to open wide as long as inlet pressure exceeds discharge pressure. Should pressure reversal occur, control tubing in the valve carries back pressure to the bonnet forcing the valve closed. Also available as the 94-1 Check With Opening Speed Control; the 94-2 With Closing Speed Control and the 94-3 With Opening and Closing Speed Control.
This is your best option to prevent water hammer, siphoning, and destruction of the pump.
RE: Pumped Network with Pipes Lower than Source Tank
Although I am new to this site,I have been in the pump industry long enough to know that introducing air into the pump in a NO No. You may want to read again the original post that the proposed goose neck with the air valve is install at the down stream ( discharge side)of the pump. Not at the suction piping.
This probably what led you to say the valve will not work near atm. pressure.
Phase separation in a pipe line is only harmful if it create a vacuum in the process and cause the separated liquid columns to collide again.
I am not a water hammer expert, but I do know what causes water hammer or pressure surge in a pipe line when the pump is suddenly shut down in a full flow.
The pump internal resistance slow down the flow of the water from suction while the water in the discharge pipe continue moving forward due to its momentum and a phase separation occurred.
Installing a auto closing valve at the pump suction line will further worsen the problem.
One of the old method to mitigate the phase separation is by increasing the inertial of the pump and driver by adding flywheel to prolong the coasting time of the pump.
You may also want to take a look again how the series 94 valve work. Are you still proposing it to be installed and how at the suction piping and how can it prevent the draining of the tank when the pumps are stopped?
Melkody,
As I suggested earlier, you may want to ask the moderator to move the whole thread to the pump engineering forum if posible to get more response.
RE: Pumped Network with Pipes Lower than Source Tank
One should be aware that introducing air into a pipeline is also a No No and is usually avoided. The air will eventually be trapped in the pipeline at high points because the pipeline would never have been constructed with no slope to it.
In addition, if you have 2 phase flow (air and water) from the introduction of air, the capacity of the water pipeline will be reduced.
The air release valve is also not a positive method of preventing the siphoning. The original post calls for a "vaccuum breaker". Since there is pressure from the upstream reservoir, the pressure at the location of the "vaccuum breaker" may not get low enough to actually activate the "vaccuum breaker".
These hydraulicly operated valves made by Cal-Val, OCV and others are intended to:
1. Slowly open after pump start;
2. Slowly close at pump shutoff; and
3. Close rapidly as a check valve in the event of power failure.
These valves are mounted on the discharge in the place of standard check valves.
The valves act as check valves;
The valves prevent water hammer;
The valves prevent siphoning through the pump.
Read further what the valve will do. This is the linke to the correct valve:
http://www
http:
To accomplish this, the valve is electrically interlocked with the pump motor and equipped for controlled opening and closing in coordination with the pump. The 125 installs on the main discharge line of the pump.
By the way, to prevent water hammer damage when the pump power fails, the check valves are supposed to close rapidly, not slowly.
RE: Pumped Network with Pipes Lower than Source Tank
1) Air Valve
If you read again the OP stated that the source tank and pumping station are both higher than most of the draw off point and water will continued to be drawn from the pipe line by gravity after pump tripped until it is empty. He will need to install air valve at the pumping station to release the air during restart.
He also mentioned that there are already air valves installed at the high points in the network.
2)You mentioned in your 2nd May reply the the valve is to be installed in the suction line to the pump.That was why I found your reply questionable.
3)
When the pumps are running,the pump pressure will keep the air valve closed after venting of the air in the pipe line. How can 2 phase flow condition occur?
4)
The OP stated the goose neck will be above the water level of the tank.Once the pumps are stopped, water continued to drawn from the pipe line due to gravity flow. The vacuum created will allow air into the pipe line and break the siphon.
http://ventomat.com/siteimgs/air.pdf
5) Hydraulically operated check valve.
This type of valve make use of the down stream pressure to force close the valve seat. In this application, the down stream side will be in a vacuum condition if air is not admitted into the system while the up stream will have the static pressure from the tank.
Do you still think the valve will work as it suppose to?
6) [quote) By the way, to prevent water hammer damage when the pump power fails, the check valves are supposed to close rapidly, not slowly. (quote}
The fundamental of surge alleviation in the pipe line during a power failure trip is to ensure continue supply of liquid into the pipe line as long as possible to prevent or delay the formation of liquid column separation till the velocity is at it lowest possible to minimize the surge pressure. The surge vessel and fly wheel method typically work on this principle.By closing the valve immediately will cause the liquid separation to happen sooner and at higher run away velocity hence higher impact when the separated liquid columns rejoin.
The check valve are suppose to close when the forward flow ceased
and before the back flow or back pressure reaches the valve
I do agreed that the valve will help during the starting phase.
RE: Pumped Network with Pipes Lower than Source Tank
Anyone who has ever operated a pipeline or water distribution system understands from experience that you should not introduce air into the system. The air will get trapped in the pipeline at numerous high points because the pwater distribution system would never have been constructed with no slope to it. Water distribution systems are not built on level grades, the water pipe profile follows the elevation of the terrain.
I would not recommend draining the entire water distribution system as he is inquiring about.
Regarding valve location:
You can install a valve in the suction line or an enhanced check valve (pump control valve), whatever is easier and cost effective. Note that the poster has not said what size of piping is in the system, but the flow rate is quite large.
Regarding 2 phase flow:
The will enter the poster's entire water distriubtion system downstream of the "vacuum breaker" when the "vacuum breaker" opens and water draings from his "faucets". It is not just drainng at the pump. The water may also drain away from the pump as well if the piping slopes downward from the pumps and air bound the pumps.
How would you propose that it not be 2 phase flow when portions of the water distribution system are drained and refilled?
Don't know what point your are making with your response to 4:
However, here is a quote from your Ventomat article stating that these vacuum breakers and air release valves may be unreliable at low operating pressures:
"It is not possible in practice, to mass produce perfectly spherical balls and generally a working pressure of at least 1 bar is required for a ball float to deform it's resilient seat sufficiently and achieve an acceptable seal."
The point that I have made is at low operating pressues, air release and vacuum breakers will tend to be unreliable.
Regarding will the hydraulic valve still work:
If line pressure is not available, then a secondary source of pressure can be used to hold the valve (check valve, pump control valve, etc) closed. Instrument engineers typically specificy volume tanks for instances where you have no power to shut a valve.
http://www
Regarding water hammer and the need to have the check valve close rapidly, here is a quote from the Ventomat article that you reference:
"Check valves are often selected without proper thought to their response UNDER PUMP TRIP CONDITIONS i.e., when a separated column commences to rejoin. The phenomenon of check valve slam occurs due to the fact that very many check valve designs require the reversal of flow to close it; this means that the column
of water is already in motion and stops abruptly as the swing check valve closes, resulting in high transient pressures.
Pressures created in this manner are dependent on the valve design used, the initial pumping velocities and the design head of the system and can be calculated using Joukowski's equation.
IN ORDER TO PREVENT OR MINIMISE THIS PHENOMENON, A QUICK ACTING, SPRING ASSISTED DESIGN SHOULD BE USED THAT WILL REACT IN A VERY LOW MILLI SECOND TIME SPAN AND AT LOW PRESSURES TO CLOSE, WITHOUT SLAMMING BEFORE REVERSAL OF FLOW HAS OCCURRED."
RE: Pumped Network with Pipes Lower than Source Tank
"Air retention results in surge (liquid oscillation) as the water compresses the retained air to a point, whence it acts as a spring, violently oscillating the liquid.
The magnitude of the surge generated is dependent on the water flow velocity (either during initial filling or when separated water columns commences to rejoin) and the size of the entrapped air pocket on closure.
Effect of the strain energy of the surges will be cumulative and concentrated at points of weakness such as reductions in pipe class, fittings which may be of a lower standard than the surrounding pipes, near line valves or tapers and in
branches with closed ends.
Pipes may also fail structurally due to the combined effect of the surge pressures which crack protective pipe linings and the retained air pockets which promotes corrosion.
Retained air causes restrictions which lead to inefficient pipeline operation and increased electrical consumption in pumping schemes as pumps are forced to work at higher heads in order to overcome the restrictions."
RE: Pumped Network with Pipes Lower than Source Tank
The the first part of the Vent-O-mat article discussed the short coming of conventional design air valve and other surge prevention methods. The later part of shows how the CATT design air valve over come or reduce the problem.
I requote:
The fundamental of surge alleviation in the pipe line during a power failure trip is to ensure continue supply of liquid into the pipe line as long as possible to prevent or delay the formation of liquid column separation till the velocity is at it lowest possible to minimize the surge pressure. The surge vessel and fly wheel method typically work on this principle.By closing the valve immediately will cause the liquid separation to happen sooner and at higher run away velocity hence higher impact when the separated liquid columns rejoin.
The check valve are suppose to close when the forward flow ceased
and before the back flow or back pressure reaches the valve causing the valve to slam on its seat.
RE: Pumped Network with Pipes Lower than Source Tank
If the original poster does not have enough money to ensure a constant water supply and reliable power source, one would doubt that he will spend scarce capital on a more expensive pump.
To summarize,
1. The gooseneck idea is not going to work because
a. The poster will fill up his water distribution system with air which will then be difficult to remove and the air once compressed has a potential to cause water hammer problems in the distribution system.
b. Air release and vacuum breakers are unreliable at low working pressure applications (less than 1 atm pressure) which will be encountered when the pumps and power are off.
c. It is not a good practice to allow air into the water distribution system.
2. His best solution is to install an enhanced check valve where:
a. The check valve will close on power failure to:
1. Prevent siphoning.
2. Help to minimize water hammer potential on pump startup and shutdown.
3. Protect his pump by maintaining water in the pump.
3. A hydropneumatic tank is not practical at a water pumping application where the flows are as high ass 330 lit/sec.
RE: Pumped Network with Pipes Lower than Source Tank
In the event of a power failure a instant shut down valve at the pump suction or discharge will sure to cause a down surge of pressure in the pipe and hence water column separation and water hammer to follow. Go and read up the book Pumping Station Design by Garr M . Jone. Chaoter 5.7 page 5-27 and chapter 6.7 page 6-11.
A preview copy is available at the below link.
htt
BTW, Cla-Val also supply Air release/ vacuum breaker valve that claimed to alleviate water hammer/ pressure surge in the vent of pump trip
http://www.cla-val.com/pdfs/E-38VBAR.pdf
RE: Pumped Network with Pipes Lower than Source Tank
If you look above, I have also provided a link to a device that is commonly used to slow a valve closing.
However, a quick closing check valve is recommended by most knowledgeable people to prevent the water hammer and backflow in the event of pump failure.
Go and read up the book Pumping Station Design by Garr Jones page 7-7
"Ensure quick closure of the check valve before the flow can reverse to cause a slam..."
"The fast-closing check valve not only prevents reverse flow through the pump, but also provides redundant protection of the pump should the pump control valve fail to close due to loss of pressure or equipment malfunction"
http://w
"Should a power failure occur, a built-in lift-type check valve closes the moment flow stops, preventing reverse flow regardless of solenoid or diaphragm assembly position."
http://www.cla-val.com/pdfs/E-60-73.pdf
RE: Pumped Network with Pipes Lower than Source Tank
RE: Pumped Network with Pipes Lower than Source Tank
Your reply 15 May;
These hydraulicly operated valves made by Cal-Val, OCV and others are intended to
1. Slowly open after pump start;
2. Slowly close at pump shutoff; and
3. Close rapidly as a check valve in the event of power failure
.
extract from the Cla-Val cataloque.
If power failure occurs when valve is open,
the built-in check valve "J" closes immediately to prevent reverse flow.
Extract from Valmatic article page 17
But the rapid closure of either the pump control valve or a fast-closing check valve in a
long piping system poses a dilemma. It was previously calculated that the 8 in. valve must
stroke in 55 seconds to prevent an excessive surge. On the other hand, the valve must close in 5
seconds to protect the pump after a power failure
RE: Pumped Network with Pipes Lower than Source Tank
And so I presented at least 5 independent and separate references above to dispute your water hammer ideas.
Pumpsonly posted "You started off suggesting to install the valve at the pump suction which is against the practice."
bimr actually posted "Have you considered the installation of an energize to open fail close valve in the suction line to the pump?
How does "in the suction line to the pump" turn into "at the pump suction"
bimr posted "Regarding valve location:
You can install a valve in the suction line or an enhanced check valve (pump control valve), whatever is easier and cost effective. " and further "His best solution is to install an enhanced check valve"
To summarize,
1. The gooseneck idea is not going to work because
a. The poster will fill up his water distribution system with air which will then be difficult to remove and the air once compressed has a potential to cause water hammer problems in the distribution system.
b. Air release and vacuum breakers are unreliable at low working pressure applications (less than 1 atm pressure) which will be encountered when the pumps and power are off.
c. It is not a good practice to allow air into the water distribution system.
2. His best solution is to install an enhanced check valve where:
a. The check valve will close on power failure to:
1. Prevent siphoning.
2. Help to minimize water hammer potential on pump startup and shutdown.
3. Protect his pump by maintaining water in the pump.
3. A hydropneumatic tank is not practical at a water pumping application where the flows are as high as 330 lit/sec.
RE: Pumped Network with Pipes Lower than Source Tank
Thank you very much for your contribution. I am really proud of being part of this forum as it contains smart people like you..
The attached figure helps describing the system better. I feel that the enhanced check valve will never be able to close after power failure as water continue to flow from the source tank through the pumps.. In order for the automatic check valve to close, the DS pressure should be higher than the US pressure so it can be directed to the valve helmet and push the piston down. Such condition may never happen so I thought of the gooseneck solution.
Air will enter the distribution network anyway; if not from the gooseneck, it will enter from other air valves installed at other high points in the system.. Special precautios should be considered while filling the line again of course to prevent water hammer as you mentioned.. The pumps will always be submerged (no air shall enter the pumps)..
RE: Pumped Network with Pipes Lower than Source Tank
Another option may be to use a float operated valve. This would consist of a float, valve, and mechanical linkage between the valve and float. As the water level drops in the reservoir, the valve will close.
RE: Pumped Network with Pipes Lower than Source Tank
1) How high pressure do you expect a vacuum breaker valve to work?
2) When the pump is running , the pressure at the highest point A minimum 20PSIG + 20 meter(29 PSI) height above the tank water level.
Therefore the air valve is seeing 49 PSI. Is this enough to close the valve?
3) New proposed float valve in tank. At what level it is suppose to shut the valve? What would happen if the level drop down to the set level and shut the suction line when the pumps are running?
4)How does "in the suction line to the pump" turn into "at the pump suction"
This only prove how much you know about pumps.
RE: Pumped Network with Pipes Lower than Source Tank
I used to know that high quality vacuum breaker valves fully open at a pressure differential of 0.05 bars (negative).. the steady state pressure of the line will be enough to seal the valve of course.
The problem with the float valve you have mentioned is its setting. The water level in the source tank is not constant. If we set the valve to close when the tank is full, it will close even when the pumps are in operation, this will cut the water supply prematurely while the the tank is not empty.. if we set the valve to close when the tank gets empty, it will not close if power failure occurs when the tanks are full and flow will not stop from the tank through the pumps.
Uptill now am convinced with the gooseneck option. The vacuum breaker valve is just needed to break the syphon..
The problem that remains un answered is how to fill back the lines without having excessive transient pressures. The control panel at the station will tend to operate all the pumps in the station as all the pressure is now lost due to power failure. Any ideas on how to do set the operation sequence of the pumps??
RE: Pumped Network with Pipes Lower than Source Tank
melkordy (Civil/Environme)
You are expecting the air release and vacuum valves to function at operating pressures as low as 100cm. Note that typical air release and vacuum breakers are not designed to operate and will be unreliable at working pressures as low as this. The vacuum breaker may not open until the water drops somewhat in the source tank. You should increase the 100 cm height to at least a meter.
In addition, point A is 20 meters above the proposed pump. So at the beginning of the power failure, you will initially have backflow conditions from point A to the pump or to the other demand points.
In order to fully understand what you are doing, and develop a reasonable control scheme, it would be helpful to know the following:
Your total flow is 330 liters/sec with 6 pumps. That would make the pump suction and discharge piping approximately 500mm diameter pipe. It that correct?
What is the use of this water system? Is it potable water or irrigation? Note that different equipment will be used for potable water systems than irrigation systems.
Are the demand points neighborhoods or fields? You said they are faucets? This flow is much too large for faucets.
What is the height and volume of the source tank?
What is the control scheme of the water tank? If you install a vacuum breaker, you will not have any control over the height of the source tank. The source tank water level will remain the same once the vacuum breaker opens. If the tank is full, it will stay full. If the tank is low, it will also stay low. The vacuum breaker effectively takes the water source tank out of service.
RE: Pumped Network with Pipes Lower than Source Tank
You are correct, the pipes are 500mm diameter. The network is distributing potable water for municipal and industrial used for a factory area. I meant by the faucets to just describe demand points connected to the network (but they are not really faucets as you mentioned).
As you mentioned, I will have backflow after power failure from point A but it will only last for few moments and the check valve will open again when the nwtwork starts draining. Also I need to install a hydropneumatic tank at the station and connect it to the piping just upstream of the gooseneck. The vessel is intended to decelerate the liquid more slowly after failure. The gooseneck with the vacuum breaker will also function to prevent the vessel from loosing all its water like the source tank.. do you agree with this?
The source tank is 10000 cubic meters in volume (storage for 5 days at peak consumption). The depth of water in the tank is only 3 meters.
As youu mentioned, the vacuum breaker will take the source tank out of service. I would like to add that this will happen when the pumps are off all pressure is lost only. Otherwise, the pumps are operating and keep the network pressurised all the time.
The peak flow of 330 lit/sec requires all 6 pumps to operate. At anaverage flow of 167 lit/sec only 3 pumps are sufficient. When there is no demand, the pumps shall just keep the network pressurized. the pressure felt just downstream the pumps is what will trigger the control panel to operate 3 or more pumps. The problem is that when power is down, pressure shall drop almost to zero at the pumps. This will make the control panel operate all 6 pumps once power is back. This is not acceptable, we should carefully fill in the lines (slowly) to avoid high transient pressures. Any ideas how to set the controls
Your help is highly appreciated.
RE: Pumped Network with Pipes Lower than Source Tank
Pump and motor controls are seldom programmed to auto start upon resume of power supply.
If it is done so, you can add timers to the starter panel of each motor to spread out the starting process over a period that you think is comfortable. If you are using PLC, it is even easier.
RE: Pumped Network with Pipes Lower than Source Tank
A few remarks on your system.
1. Regarding draining the system.
a. You should be aware that you will experience increased pipe corrosion as a result of draining your water system. The air that enters will cause corrosion and microorganisms will thrive.
b. We never drain water distributions system because it is so difficult to disinfect potable water systems again after the system is drained. You will be introducing contaminants into the potable water system when the system drains.
c. As the linked article notes, it is necessary to fill water distribution very slowly to avoid water hammer, air pockets, etc. The article notes that when filling a water system, air pockets may generate pressures may be up to 10 times normal. This may cause piping blowouts.
2. Have you considered a standpipe? Constructions of a standpipe will greatly simply the control of your water distribution system, especially if you experience frequent power failure or unreliable power supplies.
3. Do you have access to low cost labor? If so, you can get by with manually operated valves. Instead of an automated valve to shut the system down in the event of a power failure, you can have a worker shut the valve(s) manually.
If you system does drain empty, you will have to do a slow startup and refilling of the water system anyway.
You can stop the siphoning with the use of a manual valve closed by a worker.
4. The current practice to control pressure in a water distribution system when you do not have an elevated storage tank is to use variable speed drives on the pumps.
5. Least expensive method to control the forward siphoning..
From the map of your system, one would not expect big issues with water hammer when the pumps fail. The issue with the system draining and refilling will be a much larger headache.
The most inexpensive method to control the siphoning is to install a valve that will automatically (slowly) close on power failure. Such a valve is spring to close, power to open. The valve should energize to open when the pumps are operating.
The valve can be installed and will work in a number of locations, but it is probably best to install it downstream of the pumps.
The valve will probably cost less than the gooseneck and vacuum breaker/air relief on a 500 mm pipe.