Adjustment procedure for this pilot-operated Pressure Reducing Valve? 2

[Ed H.]

I am having trouble getting a pilot operated PRV to operate as I think it should. This 3 inch PRV is installed in a private, gravity-fed domestic water supply system on a mountain. There is storage tank at the top of the hill and home sites served by the system are located at various locations going down the mountain. The PRV is located half way down to keep the line pressure manageable. The upstream pressure at the PRV is approximately 120psi. I would like to reduce the downstream pressure to around 40psi.

The problem i have is when a larger downstream demand pulls water, the downstream pressure at the PRV will drop to zero and the PRV locks up in the closed position, even after the demand subsides. Then, the only way to start flow through the PRV is to adjust the red valve clockwise (closing). I would like to confirm the proper sequence/procedure for adjusting this valve. Thank you!

 

[Compositepro]

Some datasheets on the valves would help a lot. Things do not look right.

It appears that water should flow from left to right. The pilot regulator should get its pressure from the up hill side. The pilot regulator does not appear to be a self-relieving type so that if its output pressure gets too high it can relieve the excess pressure to the environment. Since it cannot do this, it will lock closed. Unlocking the valve will require that the excess pressure be vented. Opening (not closing) the red valve will do this. It is possible that turning the red valve clockwise will open it, although that is unusual. Some vent/drain valves work this way, and the red valve should normally be closed.

You basic problem appears to be that you are using the wrong type of pilot regulator, which is not self-reliving. Your pilot regulator was designed to be used as a main supply regulator to a house. It will not prevent over-pressure if there is no flow, but when someone opens a tap in the house it will control pressure.

 

[Ed H.]

Unfortunately, I do not have any datasheet on the valve. Below is the id plate on the valve. The uphill side is on the right (green tube) and downhill on the left (white).

 

[mk3223]

You may contact the manufacturer, Zhejiang Guanlong Machinery Valve, for the valve issue and ask for the manual to verify the operation setup.
IMO, the valve was closed to maintain the upstream pressure, which was like a "back pressure" control valve.

 

[Compositepro]

http://wzguanlong.en.made-in-china....Diaphragm-Piston-Pressure-Reducing-Valve.html

The pilot regulator is , in fact, a standard water pressure regulator with an inlet strainer. It is, however, being used in a somewhat unusual way. When the downstream pressure drops below set point, the the pilot regulator opens and drains water from the dome of the main valve, causing it to open. The dome is filled by water from the upstream piping through the red-handled valve. There may be a fixed restrictive orifice in-line with this red valve, or the valve may be the only restriction. Increasing the resriction of the red valve by closing it, will slowdown how quickly the main valve can close, probably to limit waterhammer.

When the downstream pressure reaches setpoint, the pilot valve closes and stops draining water from the dome which causes the main valve to close due to flow though the red valve filling the dome.

So for your application, the red valve must not be fully open or fully closed, but adjusted for your flow conditions. How to find the "optimum" setting, I do not know. It will be influenced by the upstream and downstream pressures, and the desired flow-rate. If you have a high upstream pressure or a low desired downstream pressure the red valve will need to be more closed.

The main valve will not be able to open if the red valve is opened too far, which is the problem that you are experiencing. If you completely close the red valve, the main valve will not be able to close.

 

[Ed H.]

Compositepro, Thank you so much for your help! Your explanation of how the valve operates is very helpful and fits with what I am seeing.

 

[LittleInch]

I agree with composite pro. At low pressure the spring would also come into play closing the valve probably at around 1 bar.

The reason your valve doesn't reopen could be either
Red valve too far open but then it shouldn't work- does it regulate pressure at normal flows?
Your regulator is blocked or has dirt in it
The diaphragm has a leak in it

Let us know what works.

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