Check Valve

[luudee]

 

Thanks for all the replies guys! Your persistence and suggestions are very much appreciated!

 

OK, so I will move the Check Valve to the Pump Inlet. 

 

But I still would like to find a better quality Check Valve. Many have suggested grundfoss and

such, I will have to see if I can find a local supplier ...

 

But I think any stainless steel valve, in general, should be better than brass. The size (2") will be a challenge.

 

So the hunt for the Check Valve is still on !  :)

 

Many Thanks,

rudi

 

[Pib]

Why 2"?  The CH8-50 only has a 1.5" inlet and 1.25" outlet.  

 

Maybe you are thinking of installing a 2" check valve (current one maybe) in a 2" pipe leading to the pump but the 2" pipe is reduced to 1.5" when connecting to the pump?

[Artisi]

1 hour ago, luudee said:

 

Thanks for all the replies guys! Your persistence and suggestions are very much appreciated!

 

OK, so I will move the Check Valve to the Pump Inlet. 

 

But I still would like to find a better quality Check Valve. Many have suggested grundfoss and

such, I will have to see if I can find a local supplier ...

 

But I think any stainless steel valve, in general, should be better than brass. The size (2") will be a challenge.

 

So the hunt for the Check Valve is still on !  :)

 

Many Thanks,

rudi

 

Rudi, this is the inlet to my Grundfos, it's been installed and running for nearly 6 years. It is nearly the same as NRV photo I posted previously  - supplied by Grundfos with the pump. 

I think a wise and correct move in relocating to the inlet. 

[Pib]

Rudi, 

   Just one more question for you regarding that check valve (non return valve) on the pump's output.  Is it "directly" on the pump's output or is it in a location that hooks to piping coming from your water source (i.e., tank, soi line, etc).  

 

Like in below picture from a Hitachi pump manual you will see a check valve that's on the pump's output side but it's not directly on the pump output and whose purpose is to block pump pressure from feeding back into the soi line and allow the soi line water to come through if the pump is dead...broke....etc.   The check valve is in a position to where when the pump is running/has the lines pressurized it prevents water coming directly from the soi line.  But if the pump is say turned off...dead..broke...etc., then it's not generating any output pressure (3.5 bars) and then incoming low pressure say from the soi line which is probably way less than 1 bar allows the check valve to open to provide water to the house although at a low pressure from the soi water line.   I have such a check valve setup on my Mitsubishi pump....pump dead broke, etc., the soi water line pressure is allowed to take over feeding water to the house.

 

I don't think you every clarified or provided a picture exactly where your check valve is located on the output side of your pump.   If it's being used like in below image then its OK-fine and the valve is staying shut to prevent backflow into the soi line (or whatever your water source is) as long as there is any pressure on the pump output side....pump on or off.   I also say even when off  because when the pump turns off you still have pressurized lines which would keep the check valve shown below closed (not opening, closing, slamming shut)...since it's not opening or closing it can't break like yours has been breaking. 

 

Yeap, would be good to have a clearer description of where your check valve is located....but right now since it failing it sure sounds like it's directly on your pump's output line before that line possibly goes to any other junctions.

'

[sipi]

A check valve on the suction line won't be subjected to pump discharge pressure so try a cheaper one first.

[luudee]

14 minutes ago, Pib said:

Rudi, 

   Just one more question for you regarding that check valve (non return valve) on the pump's output.  Is it "directly" on the pump's output or is it in a location that hooks to piping coming from your water source (i.e., tank, soi line, etc).  

 

Like in below picture from a Hitachi pump manual you will see a check valve that's on the pump's output side but it's not directly on the pump output and whose purpose is to block pump pressure from feeding back into the soi line and allow the soi line water to come through if the pump is dead...broke....etc.   The check valve is in a position to where when the pump is running/has the lines pressurized it prevents water coming directly from the soi line.  But if the pump is say turned off...dead..broke...etc., then it's not generating any output pressure (3.5 bars) and then incoming low pressure say from the soi line which is probably way less than 1 bar allows the check valve to open to provide water to the house although at a low pressure from the soi water line.   I have such a check valve setup on my Mitsubishi pump....pump dead broke, etc., the soi water line pressure is allowed to take over feeding water to the house.

 

I don't think you every clarified or provided a picture exactly where your check valve is located on the output side of your pump.   If it's being used like in below image then its OK-fine and the valve is staying shut to prevent backflow into the soi line (or whatever your water source is) as long as there is any pressure on the pump output side....pump on or off.   I also say even when off  because when the pump turns off you still have pressurized lines which would keep the check valve shown below closed (not opening, closing, slamming shut)...since it's not opening or closing it can't break like yours has been breaking. 

 

Yeap, would be good to have a clearer description of where your check valve is located....but right now since it failing it sure sounds like it's directly on your pump's output line before that line possibly goes to any other junctions.

11

 

Please see below drawing. It's quite a simple system. All pipes are 2" PVC. About 50 CM from

the tank to the pump, another 50 cm from the pump to the Check Valve.  The Pressure tank and

pressure switch are about 3 meters away ...

 

 

rudi

 

[sipi]

Yep. Standard check valve on the suction side, (remove discharge one)........

job done.

[Pib]

yea, put the check valve on the suction side.

 

[Artisi]

25 minutes ago, sipi said:

A check valve on the suction line won't be subjected to pump discharge pressure so try a cheaper one first.

Actually the whole system  from pump side of the NRV to discharge pipe is always at the variable system pressure as controlled by the pressure tank,  draw off, and pressure control switch.  

[luudee]

3 minutes ago, Pib said:

yea, put the check valve on the suction side.

 

 

 

I hear you guys !  :)

 

Can somebody please explain to me the mechanics,  how a check valve on the suction side will be better than on the outlet side ?

I am just curious to understand ...

 

BTW, the tanks are about 2 meters tall, so there is quite some gravitational pressure at the pump inlet ...

 

Thanks !

rudi

[sipi]

2mtrs head pressure is only 20 kPa. Discharge pressure of 350 kPa is quite a pump ratio (12 to 1).

Just finished night shift so someone else can explain.

You need to look at the whole pump cycle to see what is going on.

Either way, a check valve slamming shut and destroying itself isn't a good design.

[Pib]

The pressure at the bottom of a 2 meter tall tank is only 2.8 psi/0.2 bar.

 

The main reason to have check valve on the suction side is to prevent the pump from loosing prime if it don't have it's own internal check valve.   Also, to prevent backflow into the water source such as the tank, soi line, well hole which might carry some contamination from the pump.

 

Now in your case as long as you still have water in your tanks you wouldn't lose pump prime.  If your tanks wet dry and go pretty close to the bottom you would probably lose pump prime and unless the pump is self-priming it couldn't get  water flow going.  And for folks on soi lines that go dry or well holes is easy to lose prime.   People on well holes will probably have a footer valve which serves a similar purposes to the check valve in that the footer valve prevents the suction side from loosing prime as long as there is water to be sucked from the well.

 

I think you said before when you check valve failed your pump would run even with no taps turned on.  That's a good indication the pump is losing prime because of pressure loss through the pump which caused the pump to turn on even though no water was being draw anywhere by you.

[canuckamuck]

2 hours ago, luudee said:

 

I hear you guys !  :)

 

Can somebody please explain to me the mechanics,  how a check valve on the suction side will be better than on the outlet side ?

I am just curious to understand ...

 

BTW, the tanks are about 2 meters tall, so there is quite some gravitational pressure at the pump inlet ...

 

Thanks !

rudi

Well for one thing the check valve is in the way of pump flow, so it is lowering the efficiency of your pump. The next issue is that when the pressure goes down and the pump gets the signal to start working, it has to force that check valve open because it is still under pressure (whatever pressure the the pressure switch is set to). For example, if your switch is set to call for water at  2 bar. Your pump has to push more than 2 bar just to open the valve. That little battle between open and closed is beating up your check valves. Check valves should last years, even cheap ones.

Now if you put that check valve on the other side of the pump, or just get rid of it all together (I don't have one because I have a two tank setup like you) there is no battle going on and the pump will be more efficient too.

[Artisi]

1 minute ago, canuckamuck said:

Well for one thing the check valve is in the way of pump flow, so it is lowering the efficiency of your pump. The next issue is that when the pressure goes down and the pump gets the signal to start working, it has to force that check valve open because it is still under pressure (whatever pressure the the pressure switch is set to). For example, if your switch is set to call for water at  2 bar. Your pump has to push more than 2 bar just to open the valve. That little battle between open and closed is beating up your check valves. Check valves should last years, even cheap ones.

Now if you put that check valve on the other side of the pump, or just get rid of it all together (I don't have one because I have a two tank setup like you) there is no battle going on and the pump will be more efficient too.

You need a check valve on the inlet otherwise the system has no way of staying pressurised, once the pump was signalled to stop at the pre-set pressure, the system pressure would immediately decay via the pump inlet to the tank. 

 

Everyone seems to miss the point that the pressure system is composite system, commencing at the pump inlet side of the NRV, the pump, the pressure tank,  and the pipework. It is maintained under the pre-set pressure until a tap is opened, the tank then maintains flow until the pressure drops to the low set point bringing the pump online until the pre-set pressure is again achieved. 

 

 

[canuckamuck]

34 minutes ago, Artisi said:

You need a check valve on the inlet otherwise the system has no way of staying pressurised, once the pump was signalled to stop at the pre-set pressure, the system pressure would immediately decay via the pump inlet to the tank. 

 

Everyone seems to miss the point that the pressure system is composite system, commencing at the pump inlet side of the NRV, the pump, the pressure tank,  and the pipework. It is maintained under the pre-set pressure until a tap is opened, the tank then maintains flow until the pressure drops to the low set point bringing the pump online until the pre-set pressure is again achieved. 

 

 

Well I don't have a check valve (NRV) because there is one in the pump itself on the inlet side. My water comes from a tank just like the OP. But if the pump doesn't have one then yes it would be essential.

Edited May 13, 2017 by canuckamuck

[Artisi]

14 minutes ago, canuckamuck said:

Well I don't have a check valve (NRV) because there is one in the pump itself on the inlet side. My water comes from a tank just like the OP. But if the pump doesn't have one then yes it would be essential.

In this case the OP has a Grundfos CH pump that doesn't include a inlet check valve. 

[Wirejerker]

Your premature failures is caused by the wrong valve for your application. The swing type of check valve relies on gravity or reverse flow to close. When the pump stops the water flow reverses causing the valve to close and the momentum of that reversing water hit the closed valve that's your water hammer damaging the valve. The better choice of check valve is a non slam valve with is a disc closed by a spring and the close before the water reverses direction. You may think the valves are not robust enough but it is the swing type causing the problem that contributes to is own demise. I have to agree with you the check valve will work either side of the pump in that setup.


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[Pacificperson]

Maybe lowering the operating pressure settings would help. If the pump runs continuously with a failed check valve, then it seems like it is being over worked.

[luudee]

47 minutes ago, Wirejerker said:

Your premature failures is caused by the wrong valve for your application. The swing type of check valve relies on gravity or reverse flow to close. When the pump stops the water flow reverses causing the valve to close and the momentum of that reversing water hit the closed valve that's your water hammer damaging the valve. The better choice of check valve is a non slam valve with is a disc closed by a spring and the close before the water reverses direction. You may think the valves are not robust enough but it is the swing type causing the problem that contributes to is own demise. I have to agree with you the check valve will work either side of the pump in that setup.


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Thank you for your message!  What do you think of the ball type check valves, they too

have a spring but are made from PVC ... or do you think the disc type is better?

 

Thanks,

rudi

[Pacificperson]

Rudi, I can't answer your question about ball versus disk check valves, but I have two suggestions. First since your pump has a 1-1/4 in discharge, that you locate any spring operated valve in this line. A two inch valve at 50 psi has about 150 lbs of pressure on it when it is closed, but a 1-1/4 valve will be subjected to much less force on it (a little over 60 pounds). Second, I had similar sized pumps but under suction and when I  used a spring type check valve on the suction line, the pump could not develop enough suction to open it. It worked fine when I changed it to a flapper type valve. So, you might want to try a spring operated 1-1/4 valve on the pressure side of your pump.

Edited May 13, 2017 by Pacificperson
clarity

[Wirejerker]

 
Thank you for your message!  What do you think of the ball type check valves, they too
have a spring but are made from PVC ... or do you think the disc type is better?
 
Thanks,
rudi

The best valves to use would be those used by the pump manufacturers as they want the best performance for their pumps.


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[Artisi]

From the Grundfos CH installation manual. 

Pretty clear where the NRV should be positioned. 

[sipi]

11 hours ago, Artisi said:

Actually the whole system  from pump side of the NRV to discharge pipe is always at the variable system pressure as controlled by the pressure tank,  draw off, and pressure control switch.  

 Correct. In my haste  (after night shift) I meant to say that a check valve on the suction side won't be subjected to the operating  pressure as the discharge side 

A check valve on the suction will open and close at 20 kPa.

A check valve on the discharge will open and close at 350 kPa.

In a nutshell. 

[sipi]

Rudi. If you insist on using a check valve on the discharge side, then a stainless boiler feed pump disc valve is the only way to go.

I think I have a reconditioned one rated at about 20 bars (or more) I can send you. They are damn expensive new and even on boilers they fail after a while.

 

Edit..

It will still slam shut at 350 kPa and hammer your pipework but will last a lot longer that the ones you are currently using.

Edited May 13, 2017 by sipi

[Wirejerker]

 

A check valve on the suction will open and close at 20 kPa.

A check valve on the discharge will open and close at 350 kPa.

In a nutshell. 

 

Thanks Sipi

That's won me around to put it on the suction side

 

 

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[Artisi]

Let's wait and see what Rudi finally decided on -  hopefully he posts some feed-back on the outcome. 

[Artisi]

3 hours ago, sipi said:

 Correct. In my haste  (after night shift) I meant to say that a check valve on the suction side won't be subjected to the operating  pressure as the discharge side 

A check valve on the suction will open and close at 20 kPa.

A check valve on the discharge will open and close at 350 kPa.

In a nutshell. 

A NRV on the discharge side will open at a pressure which equals -   the area of the disc X the system pressure (which is the pre-set cut in pressure ) the opening force on the valve will be the area of the disc X the pump discharge pressure, the pump discharge pressure is higher than the system pressure. 

A x P (pump) > A x P (system) 

[Wirejerker]

A NRV on the discharge side will open at a pressure which equals -   the area of the disc X the system pressure (which is the pre-set cut in pressure ) the opening force on the valve will be the area of the disc X the pump discharge pressure, the pump discharge pressure is higher than the system pressure. 
A x P (pump) > A x P (system) 

The differential pressure when the check valve open/closes is still only in the order of 20 kpa . The only time it has the system pressure is when the pump is stopped


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[sipi]

With the check valve on the suction it will open when the pump kicks in and suction pressure at the pump drops below tank head pressure (20kPa).

With the check valve on the discharge it will open when the pump kicks in and discharge pressure goes above system pressure (350kPa).

And vice versa when it stops.

Draw a few pictures and think about it. 

Anyway up to Rudi.

[Gary A]

You can tell a lot about a check valve just by looking closely at it regardless of who manufactured it. I put one in ten years ago and it is still working fine. The entire valve should be brass, Stainless steel would be good but I have never seen one in Thailand. The little swinging gate should also be brass and the rubber washer should be stretched over a protrusion on the little gate so that it would be very difficult for it to come off. Finally the hinge pin should be stainless steel, How do you check that? A magnet will quickly tell you. There are other designs and they may be OK but I trust the old fashion swinging gate type more. Don't be afraid to take it apart. A large nut covers the swinging gate. You can see how the valve is made by removing that nut.