Regulator - Hunting Downstream

I would suspect that it's from pressure waves. Is there an accumulator nearby? If not, try adding one with small orfices to minimize pressure fluctuations, and put the pressure regulating valve in that circuit.

thanks.

What do you mean accumulator?

Also, can you help me in expanding the "hunting" downstream? what causes it?

Four possibilities:

1. The PCV is oversized for the application.

2. Something internal is sticking.

3. The valve passage/seat/plug/disc/etc. is eroded.

4. Leaking diaphragm.

Accumulator means nothing more than a tank or other relatively large volume buffer to minimize pressure fluctuations. (In refrigeration systems, it's a tank to collect liquid and has enough volume to allow part of the liquid to return to a gaseous state before it returns to the compressor.) Don't think much about my use of the term -- it just means tank.

On the other hand, the flow of compressed air into the tank should be restricted so that rapid pressure fluctuations cannot occur. The main tank is usually close by the compressor and very large with respect to the volume of the compressor cylinder(s) and performs such a function more or less automatically. From your description, it sounds like you may not even have a "main tank," or if so, it isn't located near the compressor.

Hope that clarifies.

I suspect Energygod is correct, use 2 PCV's the pressure drop range is to great for one PCV to handle, I also suggest you check the capacity, because if the capacity of is the valve is to large then you will get instability

You dont say if your valve is pilot regulated or just a run of the mill pressure reducer. Either way your upstream pressure is enormous in comparison to your down stream. I would rather use a common ( run of the mill ) pressure reducer to drop the pressure down to, 2-2.5 bar, and then a pilot regulated, good quality, reducing valve for the final low oressure. Make sure that there is no moisture in your line. Moisture will play havoc with any low pressure regulator, good quality or not.

I see Energygod have given similar advice. Nice to be in like minded company at opposite ends of the world.

Thank you for the thank you, however we would like to know whether any of the advice solved your problem.

Energygod is correct, use a second regulator supplied from the first preferably one with a large diaphragm to give it good control for such a small pressure range. Or a dual stage regulator might do the trick.

stick with the tried and trusted use 2 PCV's in series, the 2nd one to regulate down to 0.35barg should ideally be a pilot operated one for such low pressures. After reading all the posts and asimilating the knowledge put forward by all the esteemed gentlemen, I am pretty sure this solution will do the trick and provide you with a stable pressure and feed for your seal gas service

"everybody" says that I am right on, but I only got one GA. Come on guys, it's a matter of pride.

I said you were and I GA'd you

You don't say what causes the compressor to trip. Is there a pressure sensor protecting the seal from over pressure (or under-pressure).

You talk of a pressure reducing valve. In a primitive form this could be nothing more than a 'tap' (a restrictor that limits the flow by pressure drop). This type of reducer has no ability to regulate the pressure except under one set of flow conditions. At no-flow the outlet pressure equals the supply pressure.

Or maybe something slightly more elaborate like a spring loaded piston that closes as pressure rises. This type of valve usually leaks across the seat allowing outlet pressure to rise, but being primitive it cannot relieve the excess pressure. Normally the leak is minimal compared to the total flow and can be ignored.

Except in your case I guess there is no flow (pressuring a static seal) - so leakage is important - and outlet pressure rises - maybe that is why the compressor trips - until maybe the valve shuts so tight that there is no more leakage. But by then it is too late.

A more sophisticated design is required. A spring-loaded or pilot loaded diaphragm valve - or rather a 'pressure regulator' - is much more sensitive to pressure changes and usually with an exhaust relief that dumps excess pressure.

As others have said, this is what you need.

Normally to select a pressure regulator, you need to specify the outlet pressure (range), the inlet pressure (range), the flow (range) and accuracy.

I hope this helps.