Minimum allowable pressure drop across a control valve for a low pressure gas system 1

[Justice100]

Hello all,

General advice for defining a control valve DP at design flow is 0.7 bar or 30% of total system DP, whichever is higher. For low pressure gas systems the minimum of 0.7 bar can be unachievable as it is not available. Can any one point me to guidance for defining this for low pressure gas systems or is just using a DP of 30% of total DP ok even if that results in a control valve DP at design flow of for example 0.1 bar? Would this need a special type of valve or would just a butterfly valve be ok?

 

[LittleInch]

Well general advice is exactly that - general.

Low pressure regulator are something quite different.

Look up gas pressure regulator and not control valves.

Your choice of valve depends on many things such as pressure, flow, turndown, sealing at high pressure, pressure available, size, type of gas etc.

You need to be much more specific to get a more specific answer.

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

 

[shvet]

There is no a simple answer as dP depends on many factors - capex/opex, rangeability, control loop accuracy&delay, seat leakage class, local practice and tech culture etc. For example I have a positive experience with gas dP 1 psi (7 kPa) at normal operating point with wide enough operating range. dP is more of a point of a result than input data.

Consulting with a proven local vendor is the best idea.

 

[georgeverghese]

Use 30% of dynamic pressure drop at 70% of full stroke at design flow if there is no other criterion. But check that turndown requirements are met also and adjust accordingly.

 

[EdStainless]

And a butterfly valve is neither a regulator nor a control valve.
It is meant for on/off service.

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P.E. Metallurgy, consulting work welcomed

 

[Compositepro]

Butterfly valves, as in car engine throttles? Generalities are just that, generalities.

 

[LittleInch]

The think that probably still applies is that the control valve / regulator CV range which is applicable should be from low flow highest DP at about 25% closed to highest flow / lowest DP at about 75% open to give good controllability.

A butterfly valve is often used for control of low DP flows bt its CV to position open may not be applicable for your usage.

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

 

[Justice100]

Ok thanks all.