Using Two Pressure Reducing Valves In Series

[sowhatso]

Dear All ,

Due to the non availability of pressure reducing valves from 40 bar to 10 bar , I will install two valves in series the first 40-16 bar and the second 16-10 bar , Is there are any limits for the distance between both valves ?

The valves are of 2" size , to be connected to 2" steel line to take water from a 16" discharge line of booster pump that discharge water at 40 bar . the 2" steel water line is to feed the operation building at the booster station and other water hydrants

 

[stanier]

I suggest that you need a severe service valve with velocity control and you will achieve the pressure reduction in one valves.

Check out Mitech, CCI, Copes Vulcan and Flowserve (Valtek) who all manufacture such a valve.

 

[itdepends]

And don't forget that when the demand for water stops- unless you have shutoff and relief- the pressure downstream of the throttling valves will reach the upstream pressure.

 

[JimCasey]

I don't disagree with Stanier, but on the order of scale. 40 bar is not enough to justify an extravagant staged, velocity control trim. This is within ASME class 300, not a boiler feedwater recirc valve. A single-stage anticavitation cage control valve should <<contain>> any cavitation and prevent damage. "itdepends" points out correctly that metal-seated valves leak when closed, so your system needs
(1) to be using water continuously at greater than the leak rate,
(2) or, to have an additional positive isolation valve, or at least the soft-seat option since I infer that this is cool water

(3) or, a PRV downstream of the control valve.

 

[stgrme]

Another option is to install a multi-hole pressure reducing device such as those from CU Services (C500, C600 or C700) downstream of the control valve. Visit the CU Services web site at:

http://www.cuservices.net

Best of luck!

 

[JimCasey]

stgrme's comment about a fixed reduction can be quite useful and economical. When it works, it's great.

This trick works pretty well on gas, but much less well on liquids. There is extremely narrow rangeability provided with the fixed restriction. It is optimized for one flowrate, but completely ineffective if the service conditions even change by 1/2. (DP~Flow^2)

When it's right, it keeps the upstream valve from cavitating. If the flow deviates, the upstream valve absorbs more of the pressure drop, cavitates,and the cav bubbles collapse on the fixed restriction until it disappers....

But we know that the customer ALWAYS gets the process conditions right the first time and they are always eager to admit that they gave the vendor bad information and that's why the equipemnt was destroyed....Right?

 

[Ashereng]

We often use regulators in series, especially when we don't have instrument air/gas.

I am not aware that there is a required distance apart, but I usually try to at least have 20D between them, piping space allowing of course.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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