How to choose the best type of valve

[Destroyer]

Hey,

I have a question to anyone who can answer me.
I need to choose a valvetype which fits the most in my application and why.
I have a compressor who delivers a constant flow. On the other side I have clients who use a variable flow but NEED a constant pressure. I need to place a valve in a bypass so I make sure the pressure remains constant. What type of valve would be the best AND WHY. Now I use a butterfly valve but the problem there is due to the caracteristic that if I open it for 50%, 70% of the flow is blown off.

Can anyone help me on this topic???

Thanks a lot

 

[geo57]

You did not mention what kind of flow rate, or available presure drop you need for the valve. These are some of the main criteria for selecting the valve type. In most pressure control applications a globe valve with equal percentage trim is the best choice, unless a low pressure drop is required, or if flow is too great. There are also some pretty nice v-ball valves which would be an improvment over the butterfly you now have. These are ball valves with a v shaped notch which gives them near equal percentage performance. Check with your local Fisher rep. He will give you some good advice on valve selection.
Good Luck George Griggs
Sr Process Controls Engineer

 

[vpl]

I was going to suggest a globe valve with a pressure regulator, then read the word compressor and realized you might have an air (or other gas) system. Also, it somewhat depends on the size of the line and how frequently the valve has to change position. Could you provide some more details? Patricia Lougheed

 

[quark]

Destroyer!

Pressure control valves of 'ConservAir' make are best for this application. The pressure fluctuation is very narrow and is 2 psi.(A general PRV will also work but pressure drop of those are very high.)

ConservAir make valves are a costlier. You can talk to Spirax Marshall even.

You have to install these valves in main line only and not in bypass line. (forget the bypass line untill there is a problem in the mainline valve).

Regards,

 

[Destroyer]

Hello,

The flowrate is 7000 m3/hr and the inlet pressure is 7 bar
I hope this is helpful.
And yes, I work with an air system

 

[TD2K]

Is the 7000 m3/hr the flow rate from the compressor or the amount of air needed by the user or both? I'm not clear how physically this system looks. The other thing to consider in sizing and selecting a valve is the valve turndown, what is the maximum flow through the valve and what is the minimum flow through the valve and associated pressures (inlet and outlet) and temperatures.

If your customer needs a slipstream of air, you put a control valve in the line with a controller on the downstream pressure. As the customer takes more or less air, the control valve will bleed off sufficient air to keep the pressure constant.

 

[PacificSteve]

Jordan makes pressure regulating valves for liquid systems, perhaps they also have something for gases.

PS

 

[valvetech]

If you are regulating pressure with a control valve you still need the by-pass line. If you use just a control valve, it will restrict flow as the demand decreases and the pressure upstream of your valve can raise and can cause problems with your pump.
If you have a by-pass line installed, you can use a back pressure regulator in the by pass to see that the pressure in your line does not exceed what you need downstream. As the demand raises and takes more of the flow (lower pressure) the BPRV will close, as the demand lessens ( higer pressure) the BPRV will open to relive through the by-pass.
You may even be able to accomplish what you need with the BPRV all by itself.

 

[Scoob]

Butterfly valve can be configured for good control if some sensible installation considerations are made.
1. Match the Valve size to the particular conditions you will operate at most of the time.
2. If there are operating conditions's outside the valves control zone (20-70º open), add another valve piped in parallel to the original.
3. Select an actuator control that gives you the 'stiff' performance you require.

4. See our Website (undergoing development at present), for details about our 'closed loop control' actuator. It is electronic, with built in PID control, and high speed performance. The Emech ceramic disc valve offer cavitation resistance (no elastomer seats to wear out), and ANSI Cl. IV seal integrity (bubble tight) even in dirty fluids.

Contact me if you would like to discuss your applications in more detail. jbilyard@emechcontrol.com

http://www.emechcontrol.com

 

[keyardee]

Hi Destroyer
For similar situations involving steady constant supply and variable demand conditions existing in a typical manufacturing unit, it is a standard practice to pump the air/gas to a higher pressure and store them in a receiver before distributing to the using units through a pressure reducer/regulator.This practice will ensure a steady load on your comprssor and the users will get their supplies at lower pressures and variable quantiies. Of course it requires lot more details about the compressor capacity and the consumption pattern before arriving at the capacity of the receiver,supply line size and the reducing valve size.