PRV station 1

[nicolai]

Hi all,
on a PRV station on water distribution..
to my knowledge it is good practice to provide Pressure regulating valves PRV) in two paralel lines to cater for for flow fluctuations
big line to cater for high flow and small line to cater for low flow situations
selection of large line not a problem- select for expected peak / mac flow
is their in guidelines though for small prv to cater for low flow?

 

[LittleInch]

Errr - Lowest normal flow perhaps?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

The answer will depend on your flow requirements and the particular valve selected.

Suggest you run this by Cla-Val or Singer representative.

Cla-Val

Singer

 

[TugboatEng]

Just thinking outside of the box here, why not size the pressure regulating valve for the small line and use bypass valves to get to the large flow when it's needed. For example from 0 to 250 gallon per minute you would operate on the pressure regulating valve only. for 250 to 500 gallon per minute you would operate and one wide open bypass valve and the pressure regulating valve. I guess it depends on how responsive you need the system to be. This system is commonly used on steam turbine throttles where a combination of fixed nozzles and one regulated nozzle allow for a very wide range of operating conditions.

 

[TBP]

You might consider a pair of half-capacity PRVs, and slightly stagger the set-points. When one valve cannot keep up with the demand, the pressure falls slightly, and the second valve starts to throttle open. The reverse happens on falling flow - as the downstream pressure begins to rise, the second valve throttles-in and may close, depending upon the load. I've used this arrangement on steam PRV stations a number of times.

 

[georgeverghese]

PRV does not give you good turndown - dont remember what turndown you get with these - ask the PRV vendor. For better turndown, use a controller / control valve set. Standard control valve station should give a turndown of say 25:1 on flow. For even better turndown, use a split range set - talk to a process control engineer. I dont think you need split range, unless this is some special application.

 

[Valvecrazy]

The low flow bypass of a PRV needs to be sized to handle the flows low enough to cause cavitation in the larger valve. Anything below the minimum safe flow of the large PRV needs to be handled by the smaller PRV on the bypass.

 

[bimr]

Design Considerations for Pressure Reducing Valve Stations In Domestic Water Systems

Correct Sizing of a Pressure Reducing Valve

A couple of typical examples where there can be more than 1 "setting":

1. Some make/models of PRVs have limited flow ranges (typically older ones), and instead 2 PRVs, one small...one large, are installed in parallel, to give a wider controllable flow range. The small one takes care of normal and low flows, and has the highest set-point, with the large one catering for peak flows, but has a lower set-point (it only starts to operate when the small PRV can no longer maintain its set-point). Modelling-wise, you only simulate this as 1 PRV, typically with the larger PRV's set-point (since most often simulating pressures at peak flow conditions).....but there are many exceptions to this, depending on how they actually operate, what their functions are, and what scenarios modelling wise you are interested in.

2. Typical new PRV installations in a water utility network in developed countries (but seeing a lot now in developing countries as well) now often has a separate pilot controller (eg. Driven by a stepper motor), or the pilot is removed entirely and replaced by pneumatic or hydraulic lines with solenoid valves. Both drive the PRV downstream pressure settings higher/lower according to a logic controller on-site (or sometimes via SCADA). They give far greater control (especially for leakage management), but more costly to build and need regular maintenance. These have multi "set-points" because the controller unit is typically programmed with a flow vs pressure curve. Low pressures in low demand periods/nighttime, higher pressures when demands increase. Older controllers were simpler and typically programmed with a nighttime (low) pressure and daytime (high pressure) according to clock time.

Bentley

 

[Valvecrazy]

No matter if you use the logic controller or the standard pressure reducing pilot, you can also get these type valves with an anti-cavitation package. Instead of a regular valve seat, these valves use two cages with holes in them. One cage slides inside the other and the holes break up the flow path. These type valves can work at much lower flow raters than a standard PRV, and in most cases do not require a low flow bypass.

 

[nicolai]

thanks everyone for valued feedback
Valvecrazy
what type of PRV/ which suppliers offers anti-cavitation packages ( with the dual cage concept)?

 

[Valvecrazy]

Talk to Cla-Val.