Check Valve

grollies · May 18, 2017

Nobody as yet has addressed the fundamental problem here.

The OP's problem isn't the destruction of NRVs but rather what is causing the pressure surge every time the system shuts down.

IMHO this is probably due to the fact that he has a pump installed which is 3 x the size needed for a residential property.

The Grundfos CH8-50 has a rated flow of 8m3/hr or 133l/min. That's a big pump. The rated operating head pressure for this pump is 3.2 bar but at closed head this goes up to 4.7 bar. The maximum installation pressure at 40degC is 10 bar.

The OP states that every time he closed a tap the system hammers the NRV. But he has a pressure tank downstream from the pump which should have an accumulator to act as a shock absorber and the system should gently pressurize until the pressure switch shuts down the pump.

Two reasons for this not happening could be:

1) The pressure tank is not operating correctly;

2) The pressure tank is too small for such a big pump.

The moment a tap is closed, the system is pressurized nearly instantly to full pump head pressure caused by the large volume the pump discharges.

This would cause a pressure surge greater than the rated head of the pump.

The purpose of a NRV, be it a flap or sprung disc design , is to prevent the negative (upstream) flow of water flow and pressure, primarily to protect equipment, whether that be a pump, flowmeter or utility watermain.

The NRV is in the correct position on the pump discharge and is protecting the pump from serious damage to bearings, shaft seals, etc. caused by his system pressure surges.

The OP says he has 2 x 2,000 litre tanks whose water level is 2m above the pump suction. The pump is therefore on a flooded suction and a NRV on the suction side is not normally required.

The only time usually a suction NRV is required on an installation like this is where water supplied to the pump is held in a sump tank and the pump has to draw the water using suction head pressure. A NRV in the form of a footer valve is then supplied at the end of the suction line towards the bottom of the tank. But this is not the case here.

Ask any O&G Process Design Engineer if a NRV should be placed on the suction side of a centrifugal pump with a flooded suction and the answer will be 'no'. In addition, any fittings (bends,tees, isolation valves, etc should be a minimum of 5 x diameter of the suction pipe. For a nominal 1.5" pipe that should mean 200mm (ok, 187.5mm) of straight suction pipe going into the pump.

When the NRV fails, the pump continues to run? You sure? Even with a failed NRV, the pump must cycle on/off not run continuously? As the NRV fails water pressure will decay back through the pump until the system drops to below set pressure at which time the pressure switch will start the pump. Once the system pressurizes, the pressure switch will turn the pump off.

IF the pump runs continuously, this can only be caused by either :

The pump loosing prime - unlikely on a 4,000 litres supply with a 2m head above the pump suction, or

Water escaping the system somewhere upstream of the NRVs current position.

If the pump is primed and running, water is being pumped somewhere. Is there a return by-pass line back to the header tank?

What does the OP do when the NRV fails in the middle of the night? Run out and manually shut the pump off?

Does the pump cycle on/off during normal use? It shouldn't.

Do you have a better diagram with all pump discharge pipe included.

I assume the pressure switch is connected to the pressure tank?

Adding a second NRV to the suction line will prevent your system pressure decaying back to the water header tank if the NRV on the pump discharge fails, but not address the problem of system surges.

Moving the NRV to the suction side and letting your pump 'act as a baffle' will eventually destroy your pump.

You are buying a new NRV, hopefully 2"? You could install this on the pump suction and then use an eccentric reducer (concentric if you can't find one) to reduce down to 1.5" but make sure the NRV and fittings are installed 200mm from the pump suction connection.

Keep the pump discharge NRV in place.

I'd include a 2" gate valve downstream of the pump discharge NRV (but upstream of the pressure switch and pressure tank) and throttle it in somewhat. That should reduce the pressure surge.

Keep us all updated on what you do and what happens. Every day's a school day!

PS Put some pressure gauges in the system.

Edited May 18, 2017 by grollies

Artisi · May 18, 2017

43 minutes ago, grollies said:

Nobody as yet has addressed the fundamental problem here.

The OP's problem isn't the destruction of NRVs but rather what is causing the pressure surge every time the system shuts down.

IMHO this is probably due to the fact that he has a pump installed which is 3 x the size needed for a residential property.

The Grundfos CH8-50 has a rated flow of 8m3/hr or 133l/min. That's a big pump. The rated operating head pressure for this pump is 3.2 bar but at closed head this goes up to 4.7 bar. The maximum installation pressure at 40degC is 10 bar.

The OP states that every time he closed a tap the system hammers the NRV. But he has a pressure tank downstream from the pump which should have an accumulator to act as a shock absorber and the system should gently pressurize until the pressure switch shuts down the pump.

Two reasons for this not happening could be:

1) The pressure tank is not operating correctly;

2) The pressure tank is too small for such a big pump.

The moment a tap is closed, the system is pressurized nearly instantly to full pump head pressure caused by the large volume the pump discharges.

This would cause a pressure surge greater than the rated head of the pump.

The purpose of a NRV, be it a flap or sprung disc design , is to prevent the negative (upstream) flow of water flow and pressure, primarily to protect equipment, whether that be a pump, flowmeter or utility watermain.

The NRV is in the correct position on the pump discharge and is protecting the pump from serious damage to bearings, shaft seals, etc. caused by his system pressure surges.

The OP says he has 2 x 2,000 litre tanks whose water level is 2m above the pump suction. The pump is therefore on a flooded suction and a NRV on the suction side is not normally required.

The only time usually a suction NRV is required on an installation like this is where water supplied to the pump is held in a sump tank and the pump has to draw the water using suction head pressure. A NRV in the form of a footer valve is then supplied at the end of the suction line towards the bottom of the tank. But this is not the case here.

Ask any O&G Process Design Engineer if a NRV should be placed on the suction side of a centrifugal pump with a flooded suction and the answer will be 'no'. In addition, any fittings (bends,tees, isolation valves, etc should be a minimum of 5 x diameter of the suction pipe. For a nominal 1.5" pipe that should mean 200mm (ok, 187.5mm) of straight suction pipe going into the pump.

When the NRV fails, the pump continues to run? You sure? Even with a failed NRV, the pump must cycle on/off not run continuously? As the NRV fails water pressure will decay back through the pump until the system drops to below set pressure at which time the pressure switch will start the pump. Once the system pressurizes, the pressure switch will turn the pump off.

IF the pump runs continuously, this can only be caused by either :

The pump loosing prime - unlikely on a 4,000 litres supply with a 2m head above the pump suction, or

Water escaping the system somewhere upstream of the NRVs current position.

If the pump is primed and running, water is being pumped somewhere. Is there a return by-pass line back to the header tank?

What does the OP do when the NRV fails in the middle of the night? Run out and manually shut the pump off?

Does the pump cycle on/off during normal use? It shouldn't.

Do you have a better diagram with all pump discharge pipe included.

I assume the pressure switch is connected to the pressure tank?

Adding a second NRV to the suction line will prevent your system pressure decaying back to the water header tank if the NRV on the pump discharge fails, but not address the problem of system surges.

Moving the NRV to the suction side and letting your pump 'act as a baffle' will eventually destroy your pump.

You are buying a new NRV, hopefully 2"? You could install this on the pump suction and then use an eccentric reducer (concentric if you can't find one) to reduce down to 1.5" but make sure the NRV and fittings are installed 200mm from the pump suction connection.

Keep the pump discharge NRV in place.

I'd include a 2" gate valve downstream of the pump discharge NRV (but upstream of the pressure switch and pressure tank) and throttle it in somewhat. That should reduce the pressure surge.

Keep us all updated on what you do and what happens. Every day's a school day!

PS Put some pressure gauges in the system.

You have hit on a few interesting & correct points, however I disagree on the location of the NRV on a pressure tank system, and it would seem so does Grundfos and it appears so does a couple of other pump manufacturers who build and supply this type pump system.

There is a lot of unknowns in this system at the moment and would require a competent pump engineer you undertake a complete review, however in my opinion moving the NRV to the inlet of the pump would overcome the constant valve failure which was the original posted problem.

I fully agree about the pump being way oversized but not the reason for the failures, the tank pre-charge is unknown as it the upper / lower pressure switch settings, many unknowns.

Edited May 18, 2017 by Artisi

grollies · May 18, 2017

45 minutes ago, Artisi said:

You have hit on a few interesting & correct points, however I disagree on the location of the NRV on a pressure tank system, and it would seem so does Grundfos and it appears so does a couple of other pump manufacturers who build and supply this type pump system.

Putting a NRV, same diameter as the pump suction connection, right next to the pump is bad practice, bad design, will cause cavitation problems and impeller wear.

Just because Grundfos et al say otherwise doesn't make it so.

I think it's called 'built-in obsolescence'.

https://en.m.wikipedia.org/wiki/Planned_obsolescence

Edited May 18, 2017 by grollies

canuckamuck · May 18, 2017

Some of his problems could result from a flooded pressure tank, leaving no air cushion. But I think the water hammer is simply the result of sudden low pressure on the pump side of the check valve and 3.5 bars of pressure rushing backwards only to be slammed out by the valve.

grollies · May 18, 2017

30 minutes ago, canuckamuck said:

Some of his problems could result from a flooded pressure tank, leaving no air cushion. But I think the water hammer is simply the result of sudden low pressure on the pump side of the check valve and 3.5 bars of pressure rushing backwards only to be slammed out by the valve.

You are right that when the pump stops the 3.5 bar differential slams the NRV shut and that is my point, the pump is too big/the pressure tank too small or accumulator u/s.

But if you move the NRV to the suction you expose the pump casing, impeller, shaft bearings and seals to the pressure surge? As I said, the fundamental problem needs addressing.

Edited May 18, 2017 by grollies

Artisi · May 18, 2017

31 minutes ago, grollies said:

Putting a NRV, same diameter as the pump suction connection, right next to the pump is bad practice, bad design, will cause cavitation problems and impeller wear.

Just because Grundfos et al say otherwise doesn't make it so.

I think it's called 'built-in obsolescence'.

https://en.m.wikipedia.org/wiki/Planned_obsolescence

Cavitation is a function of net positive suction head (NPSH) not valve size or position, poor location can result in other than ideal entry conditions into the impeller eye, pre-rotation - but not cavitation.

grollies · May 18, 2017

51 minutes ago, Artisi said:

Cavitation is a function of net positive suction head (NPSH) not valve size or position, poor location can result in other than ideal entry conditions into the impeller eye, pre-rotation - but not cavitation.

Locating same-sized/under-sized fittings adjacent to a pump suction will cause impeller pressure to drop, to the point where the SVP of water entering the impeller maybe reached. This will result in the water at the impeller boiling at ambient temperature, causing cavitation and subsequent impeller wear.

Any fittings upstream of a pump suction should be at least 2 x the suction port diameter and at least 5 x suction port diameter distant from the pump.

In the OPs case, ideally he should have a 3" NRV on the suction side of the pump, reducing with an eccentric reducer (with the bulgy bit at the bottom) at least 200mm from the pump suction inlet. This is good design practice but doesn't address his fundamental problem. No-one has as yet made a relevant comment to my first post.

Edited May 18, 2017 by grollies
grammar

grollies · May 18, 2017

Sufficient LAMINAR flow into a pump suction = efficient pumping.

Restrictive, turbulent flow into a pump suction = inefficient pumping.

This argument isn't helping the OP though.

Please add your comment to his fundamental problem.

luudee · May 18, 2017

Thank you for the detailed reply grollies !

Let me try to reply in a slightly different form ...

I will address your question and make some corrections to your message only:

The OP states that every time he closed a tap the system hammers the NRV. But he has a pressure tank downstream from the pump which should have an accumulator to act as a shock absorber and the system should gently pressurize until the pressure switch shuts down the pump.

Actually, I have never said that the hammering is when I close a tap. :)

The hammering occurs when the pump stops. The pump is controlled by a pressure switch.

Two reasons for this not happening could be:

1) The pressure tank is not operating correctly;

2) The pressure tank is too small for such a big pump.

The pressure tank is a 200L (I previously said 150L, it's actually 200L)
Pressure tank, rated for this pressure and system. I do manually monitor
the air pressure in the pressure tank and adjust it if needed. The pressure
tank is not flooded or otherwise damaged.

This is a working system, it works like a charm (except for eating the NRV, lol) !!!

The moment a tap is closed, the system is pressurized nearly instantly to full pump head pressure caused by the large volume the pump discharges.

This correct - this all works!

Ask any O&G Process Design Engineer if a NRV should be placed on the suction side of a centrifugal pump with a flooded suction and the answer will be 'no'. In addition, any fittings (bends,tees, isolation valves, etc should be a minimum of 5 x diameter of the suction pipe. For a nominal 1.5" pipe that should mean 200mm (ok, 187.5mm) of straight suction pipe going into the pump.

Both intake and discharge piping are 2" ...

When the NRV fails, the pump continues to run? You sure? Even with a failed NRV, the pump must cycle on/off not run continuously? As the NRV fails water pressure will decay back through the pump until the system drops to below set pressure at which time the pressure switch will start the pump. Once the system pressurizes, the pressure switch will turn the pump off.

Yes.

No water is escaping, and the pump is still primed ... I can't explain it either ....

What does the OP do when the NRV fails in the middle of the night? Run out and manually shut the pump off?

Keep on sleeping, lol .... I'll find out in the morning. I have workers that might wake
up and turn the system off, otherwise, it will keep on running ...

Does the pump cycle on/off during normal use? It shouldn't.

If a tab is open, the pressure will eventually drop and the pump will start.

When no tab is open, no water used, the pump does no cycle ...

Do you have a better diagram with all pump discharge pipe included.

The diagram is 100% complete. :)

There is no discharge pipe, I don't even know what that means :)

I assume the pressure switch is connected to the pressure tank?

It's connected near the pressure tank on the right-hand-side pipe ...

It's location shouldn't that critical, as the pressure should be equal everywhere on the right-hand-side ...

You are buying a new NRV, hopefully 2"? You could install this on the pump suction and then use an eccentric reducer (concentric if you can't find one) to reduce down to 1.5" but make sure the NRV and fittings are installed 200mm from the pump suction connection.

I'm a bit confused, all my pipes and NRV are 2" ...

....

Keep us all updated on what you do and what happens. Every day's a school day!

Will do.

PS Put some pressure gauges in the system.

I have one next to the pressure switch!

Thank you for your time !

rudi

luudee · May 18, 2017

Guys,

here are a couple of pictures of the setup .. it is very simple ...

I'll try to add a few more tomorrow ...

rudi

sipi · May 18, 2017

That is definitely the wrong type of check valve for the discharge.

Grollies makes some good points.

A swing check opens fully with very little differential pressure and I have never seen one cause cavitation on the suction side. A spring disc check valve on the suction will definitely rattle the pump apart.

I did mention hammering to the Grundfos rep and he suggested throttling the discharg temporarily to see what happens in the system, but one thing at a time.

That is the wrong valve in the wrong place.

Edit.

As Grollies mentioned, if the hammer continues after putting a check valve on the suction then address it immediately before it damages the mechanical seal.

Edited May 18, 2017 by sipi

luudee · May 18, 2017

14 minutes ago, sipi said:

That is definitely the wrong type of check valve for the discharge.

Grollies makes some good points.

A swing check opens fully with very little differential pressure and I have never seen one cause cavitation on the suction side. A spring disc check valve on the suction will definitely rattle the pump apart.

I did mention hammering to the Grundfos rep and he suggested throttling the discharg temporarily to see what happens in the system, but one thing at a time.

That is the wrong valve in the wrong place.

Sorry, Sipi, I don't understand. I thought this is what Grollies was actually suggesting?

A swing-style NRV on the discharge ...

What did I miss ?

Thanks,

rudi

sipi · May 18, 2017

18 minutes ago, luudee said:

Sorry, Sipi, I don't understand. I thought this is what Grollies was actually suggesting?

A swing-style NRV on the discharge ...

What did I miss ?

Thanks,

rudi

You already have a swing nrv on the discharge (with the hex cap). Or that is what it looks to me on my phone with a cracked screen.

Edit. Not a lot of room to put a nrv on the suction anyway, might be why they put it on the discharge.

Either way, I have never seen a swing valve on the discharge.

Hmmmm....

I am off to bed. See what the others can chime in.

Edited May 18, 2017 by sipi

sipi · May 18, 2017

Damn now I can't sleep.

You have ordered a new stainless valve which will certainly be stronger than a brass one.

Looking at your suction line there is no room to fit, so maybe try what Grollies suggested and put in on the discharge then try to sort that hammering out.

sipi · May 18, 2017

10 hours ago, grollies said:

Nobody as yet has addressed the fundamental problem here.

The OP's problem isn't the destruction of NRVs but rather what is causing the pressure surge every time the system shuts down.

IMHO this is probably due to the fact that he has a pump installed which is 3 x the size needed for a residential property.

The Grundfos CH8-50 has a rated flow of 8m3/hr or 133l/min. That's a big pump. The rated operating head pressure for this pump is 3.2 bar but at closed head this goes up to 4.7 bar. The maximum installation pressure at 40degC is 10 bar.

The OP states that every time he closed a tap the system hammers the NRV. But he has a pressure tank downstream from the pump which should have an accumulator to act as a shock absorber and the system should gently pressurize until the pressure switch shuts down the pump.

Two reasons for this not happening could be:

1) The pressure tank is not operating correctly;

2) The pressure tank is too small for such a big pump.

The moment a tap is closed, the system is pressurized nearly instantly to full pump head pressure caused by the large volume the pump discharges.

This would cause a pressure surge greater than the rated head of the pump.

The purpose of a NRV, be it a flap or sprung disc design , is to prevent the negative (upstream) flow of water flow and pressure, primarily to protect equipment, whether that be a pump, flowmeter or utility watermain.

The NRV is in the correct position on the pump discharge and is protecting the pump from serious damage to bearings, shaft seals, etc. caused by his system pressure surges.

The OP says he has 2 x 2,000 litre tanks whose water level is 2m above the pump suction. The pump is therefore on a flooded suction and a NRV on the suction side is not normally required.

The only time usually a suction NRV is required on an installation like this is where water supplied to the pump is held in a sump tank and the pump has to draw the water using suction head pressure. A NRV in the form of a footer valve is then supplied at the end of the suction line towards the bottom of the tank. But this is not the case here.

Ask any O&G Process Design Engineer if a NRV should be placed on the suction side of a centrifugal pump with a flooded suction and the answer will be 'no'. In addition, any fittings (bends,tees, isolation valves, etc should be a minimum of 5 x diameter of the suction pipe. For a nominal 1.5" pipe that should mean 200mm (ok, 187.5mm) of straight suction pipe going into the pump.

When the NRV fails, the pump continues to run? You sure? Even with a failed NRV, the pump must cycle on/off not run continuously? As the NRV fails water pressure will decay back through the pump until the system drops to below set pressure at which time the pressure switch will start the pump. Once the system pressurizes, the pressure switch will turn the pump off.

IF the pump runs continuously, this can only be caused by either :

The pump loosing prime - unlikely on a 4,000 litres supply with a 2m head above the pump suction, or

Water escaping the system somewhere upstream of the NRVs current position.

If the pump is primed and running, water is being pumped somewhere. Is there a return by-pass line back to the header tank?

What does the OP do when the NRV fails in the middle of the night? Run out and manually shut the pump off?

Does the pump cycle on/off during normal use? It shouldn't.

Do you have a better diagram with all pump discharge pipe included.

I assume the pressure switch is connected to the pressure tank?

Adding a second NRV to the suction line will prevent your system pressure decaying back to the water header tank if the NRV on the pump discharge fails, but not address the problem of system surges.

Moving the NRV to the suction side and letting your pump 'act as a baffle' will eventually destroy your pump.

You are buying a new NRV, hopefully 2"? You could install this on the pump suction and then use an eccentric reducer (concentric if you can't find one) to reduce down to 1.5" but make sure the NRV and fittings are installed 200mm from the pump suction connection.

Keep the pump discharge NRV in place.

I'd include a 2" gate valve downstream of the pump discharge NRV (but upstream of the pressure switch and pressure tank) and throttle it in somewhat. That should reduce the pressure surge.

Keep us all updated on what you do and what happens. Every day's a school day!

PS Put some pressure gauges in the system.

Having seen the photos I agree 100 percent.

Except for the bit about sump foot valves which are obviously needed to keep the pump primed if the pump is above the water level being the only time the nrv is on the suction.

All our multi-stage grundfoss washdown and system pumps have the nrv on the suction side (as per photo) running at about 12 bar with no problems.

The only grundfoss pumps we have with the nrv on the discharge are pumps in an open loop (pumping from a tank back to the tank with branch lines) which run 24/7 to stop backflow in power failure; or pumps that pump into a vapor space so vapor can't feed back and the pump loses prime.

Other than that we have dozens of grundfoss pumps of various sized with the swing type nrv on the suction line. All designed and fitted by grundfoss.

Having seen the photos, now what?

sipi · May 18, 2017

Just had time to take s closer look at the pressure tank.

I know precious little about them, the bladder accumulators we have on site are serviced by contractors. But the ones I gave seen pulled apart are a shell with a giant rubber condom inside. The condom absorbs the pressure in the system. And the shell is filled with nitrogen so the bladder has something to expand against (if that makes sense?).

So if Rudi is "bleeding the air from the pressure tank" then he could actually be expelling the gas that is meant to be in the shell. Perhaps a tire guage on the shrouder valve on the pressure tank might indicate if all the gas is gone?

Cue Grollies....

Edit again.

Just found this online. Apparently you can pump them up with a bike pump.

https://southernswater.com.au/pressure-tanks/

Edited May 18, 2017 by sipi
insert link

grollies · May 19, 2017

9 hours ago, luudee said:

Sorry, Sipi, I don't understand. I thought this is what Grollies was actually suggesting?

A swing-style NRV on the discharge ...

What did I miss ?

Thanks,

rudi

To clarify:

The existing set-up has a 2" brass flap-type NRV on the pump discharge. Assuming it is still operational, leave it in place.

Your new s/s flap-type NRV, install on the suction side, if possible. If it won't fit, change it out with the brass one, get a second cheap brass NRV and fit these to the 2 x 2" suction lines close to the 2" tee.

I still can't figure out why your pump runs continuously when the NRV fails.......

Your Grundfos CH8-50 is a multi-stage pump, capable of 10m3/hr and max head of 10 bar. I hate to say it's too big for your application but I'll say it anyway.

Good luck with your fix, I think we are all eagerly anticipating the arrival of the new NRV

luudee · May 19, 2017

Here is a small video of the hammering ...

http://sendvid.com/5rvl9hdn

rudi

luudee · May 19, 2017

25 minutes ago, grollies said:

To clarify:

The existing set-up has a 2" brass flap-type NRV on the pump discharge. Assuming it is still operational, leave it in place.

Your new s/s flap-type NRV, install on the suction side, if possible. If it won't fit, change it out with the brass one, get a second cheap brass NRV and fit these to the 2 x 2" suction lines close to the 2" tee.

.......

Yes, the current NRV on the discharge side is holding up so far ...

So if I add a second NRV on the suction, that will reduce the hammer?

Thanks,

rudi

luudee · May 19, 2017

9 hours ago, sipi said:

Damn now I can't sleep.

You have ordered a new stainless valve which will certainly be stronger than a brass one.

Looking at your suction line there is no room to fit, so maybe try what Grollies suggested and put in on the discharge then try to sort that hammering out.

Should I send you some Xanex ?

I can figure out a way to mount the new NRV on the suction side. The pump is not

bolted down and the PVC plumbing can be easily adjusted in lengths ...

I'll try adding the new valve on the suction side when it comes ...

BTW, do these Grundfos pumps require any maintenance? Mine has been in

place since March 2008 ....

Thanks,

rudi

grollies · May 19, 2017

24 minutes ago, luudee said:

Yes, the current NRV on the discharge side is holding up so far ...

So if I add a second NRV on the suction, that will reduce the hammer?

Thanks,

rudi

Probably not.

sipi · May 19, 2017

12 minutes ago, luudee said:

Should I send you some Xanex ?

I can figure out a way to mount the new NRV on the suction side. The pump is not

bolted down and the PVC plumbing can be easily adjusted in lengths ...

I'll try adding the new valve on the suction side when it comes ...

BTW, do these Grundfos pumps require any maintenance? Mine has been in

place since March 2008 ....

Thanks,

rudi

Back at bloody work now Rudi. AlI do lately is work and try to sleep.

Our grundfoss pumps are mostly cr series, vertical multistage. These ones are practically maintenance free apart from the odd mechanical seal.

Don't forget Grollies info about the pressure vessel. Don't want to damage the pump. I would slip a tyre guage on it to see what is going on.

grollies · May 19, 2017

16 minutes ago, luudee said:

Should I send you some Xanex ?

I can figure out a way to mount the new NRV on the suction side. The pump is not

bolted down and the PVC plumbing can be easily adjusted in lengths ...

Er, your pump should be bolted down and pipework should be clamped down also to prevent movement. This could be a contributing cause of the water hammer.

16 minutes ago, luudee said:

I'll try adding the new valve on the suction side when it comes ...

BTW, do these Grundfos pumps require any maintenance? Mine has been in

place since March 2008 ....

If I were you I'd strip off the pump end and check impellers and wear rings. But if you haven't had it services in 9 years maybe time for the Grundfos fitter to pay a visit. Get them to check your pressure tank while they're at it.

16 minutes ago, luudee said:

Thanks,

rudi

RichCor · May 19, 2017

19 hours ago, grollies said:

Nobody as yet has addressed the fundamental problem here.

The OP's problem isn't the destruction of NRVs but rather what is causing the pressure surge every time the system shuts down.

IMHO this is probably due to the fact that he has a pump installed which is 3 x the size needed for a residential property.

I'm thinking the oversized pump is causing water to move at high velocity into the pressure tank. That higher velocity is then responsible for creating pressure differentials once the pump cuts off, creating a low-pressure area as it moves away from the pump while building temporary pressure in the air spring of the pressure tank. Hammer time. Goodbye swing valve.

If spring-disc pressure check valves aren't helping then what about a soft start/stop on the pump?

luudee · May 19, 2017

2 hours ago, grollies said:

Probably not.

So that means I am back to square one ! :)

Nothing will help to remove the hammer?

Rich has suggested a soft start/stop ... I thought about a soft stop ...

that should be easy to try out, just need to find one here in thailand ...

any pointers guys ?

Thanks,

rudi

sipi · May 19, 2017

Rudi.

This is the closest thing to your system we have at work.

A 2" CR Grundfoss multistage pump rated at 5.8m3/ min, 16 bar, pressure switch set at 6 bar. Hard start. Feeding a closed system. 1100kPa Grundfoss pressure tank. Swing check valve on the suction. It cycles, doesn't hammer. Basically maintenance free.

I agree with Grillies about checking the pressure tank while you are there.

Moonlover · May 19, 2017

On 5/13/2017 at 3:12 PM, luudee said:

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

I cannot, for the life of me, see any reason why there is a check valve there at all. It serves absolutely no purpose.The only way that water could flow back through it, is if the downstream line pressure became higher than the pump supply pressure.

And that cannot possibly happen because the pump is the only component in the system that is supplying the l;ine pressure in the first place.

How can the line pressure possibly go higher than the shut off pressure that the switch is set at. It would be defying the physics of hydrodynamics.

I would simply dispose of the check valve.

Edited May 19, 2017 by Moonlover

Artisi · May 19, 2017

1 hour ago, Moonlover said:

I cannot, for the life of me, see any reason why there is a check valve there at all. It serves absolutely no purpose.The only way that water could flow back through it, is if the downstream line pressure became higher than the pump supply pressure.

And that cannot possibly happen because the pump is the only component in the system that is supplying the l;ine pressure in the first place.

How can the line pressure possibly go higher than the shut off pressure that the switch is set at. It would be defying the physics of hydrodynamics.

I would simply dispose of the check valve.

And how will the system pressure be maintained without a check valve once the pump stops.

Moonlover · May 19, 2017

2 hours ago, Artisi said:

And how will the system pressure be maintained without a check valve once the pump stops.

Ah---Yes. My folly. I was assuming this was a standard domestic arrangement in which everything is all built into the pump.

I gracefully butt out!

grollies · May 19, 2017

37 minutes ago, Moonlover said:

Ah---Yes. My folly. I was assuming this was a standard domestic arrangement in which everything is all built into the pump.

I gracefully butt out!

I know what you mean. My Mitsubishi house pump has a built-in plastic spring NRV towards the suction side of the pump head.

But I still have an additional NRV on the pump discharge to protect the pump impeller and plastic parts on the pump discharge as I have two other potential feeds to the house which could in theory over-pressurize and damage the pump.

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