Piston vs Diaphram Control Valve

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Thread Starter

Yasir Anwar

Basically I want to know the comparison b/w piston and diaphragm control valve, as it is usually considered that the piston control valve gives high trust. What is the philosophy which makes it so?

I hope for a informative reply.

Yasir Anwar
Instrument Engineer
 
R
Yasir,

Thrust = Pressure x Area

Diaphragm actuators are usually limited to 30-35 PSI, whereas pistons are at line pressure. Some manufacturers use piston type valves more than others, for example Valtek vs. Fisher.

Regards,

Roy
 
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Ronald Deepak

Yasir,

What Roy mentioned is true. Diaphragm actuators are usually limited to a max. of 40-45 psi supply pressure. The other consideration is the range of valve travels that a diaphragm actuator can handle. Based on my experience, most diaphragm actuators are available for upto 4 inches valve travel. Since the actuator is expected to be a linear element, the diaphragm actuator is limited to 4 inch upto which the diaphragm has a constant area , and thereby having a linear response.

Piston actuators however are capable of producing high thrust in addition to having longer travels.

Let me know if you would have any questions.

Ronald Deepak
jronalddeepak [at] gmail.com
 
Dear Mr. Yasir,

Both the Diagram and Piston actuators have their own benefits and applications in their own place.

The Diaphragm actuator is more responsive to small changes and continuously changing process variables. For example if the signal changes from 3 psi to 3.2 psi, the diaphragm actuator will respond quickly.

Secondly a process variable that continuously changes like pressure or flow, the diaphragm is more effective in such applications. Thirdly at low pressure and small travel application the diaphragm actuator is recommended.

On the contrary, Piston actuator is applied at high pressure and long travel applications. To low signal changes e.g. if signal changes from 3 psi to 3.3 Psi the piston actuator is sluggish and does not respond. Similarly, to continuous changes the response is not as quick as that of Diaphragm.

MA Qazi
26 July 2018
 
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