Proper side of a pump to to place the valve on

[LarryAndrews314]

All,
I have a curiosity question here. I've been to a few different recreational waterparks and seen the pumping systems that provide the ride waterflow. What I'm wondering is it correct to put the valve on the output or input side of a pump? Right now I'm in China and they're putting all the valves on the input side(picture attached). I'm thinking the best side would be the output side. I was at a park in Australia where too high a horsepower pump was installed without a VFD and the engineer partially closed to the valve on the output side to temporarily stop the cavitation. What is your guys opinion? Is the difference negligible?

 

[Artisi]

A great photo of nothing, unless you are into plastic bags and blue pipe.

But to answer your question:
1. a valve on the inlet side would be used to isolate the pump from the supply side of the system should you ever want to remove it, so - there is nothing inherently wrong with a valve on the inlet side. But ensure all valves etc are located at least 5 - 10 pipe diameters back from the pump inlet.
2. likewise you need a valve on the discharge side for the same reason - to isolate the pump from the discharge side of the system.

The closing down of the valve on the discharge side of the pump to reduce flow and limit cavitation is a standard "trick" as a temporary measure if a pump has a cavitation problem - if the pump is over-specified for the application then other long term measures need to be considered like a reduction of impeller diameter.
However, you would never close down a valve on the inlet side on an operating pump as you are likely to cause cavitation.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

Ideally you want both so you can isolate the pump and remove it for repair if needed, but I'm with you that if you're only going to fit one the fit it on the output side. It reduces pressure on the seals when the pump is not running and although not recommended to use isolation valves for control, better this is done with the output valve and not the suction valve.


I note from your photo that it looks like they have an nrv on the outlet which some bright spark probably thinks does the same job as an isolation valve....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[LarryAndrews314]

Thanks for the input guys. Yes, that is an NRV on the output side. Is the difference between that and another valve the quality of the seal? I haven't seen a park yet with valves on both sides, probably for cost, which makes me curious about how messy the pump swaps are. They must have to drain the entire pool. Seems to me like there's no point in having a valve at all unless you have have one on each side of the pump.

Artisi, I did learn from your post but please save the sarcasm for something else. I'm sure what you can glean from a photo is as much a reflection of what is in your head just as much as what is in the photo. Hell, Littleinch spotted something I had to do a double take on and I was there.

 

[LittleInch]

An isolation valve is exactly that and doesn't rely on pressure difference to seal Luke an NRV does. However this would probably hold back most of the water while you changed the pump. I would never rely on it but then I work in the oil and gas industry and any sort of leak is potentially hazardous. For that reason you need the nrv on the outlet as on the suction side it would just flow out.....

Even then I struggle to see the savings from one isolation valve, but they probably consider pump failure is relatively rare or just replace it overnight.


They may well have a common isolation valve somewhere you can't see to avoid draining a huge volume.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

This may well be stating the obvious but, the NRV's are needed with more than one pump discharging into the same pipeline (header) so as not the pump back thru the other pump/s not in operating.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

It also means you can start any pump remotely without needing to go and open any valves. I'd still rather have an isolation valve both sides myself though....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

Me too, no argument there.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)