A pressure regulator is a valve that controls the pressure of a fluid to a desired value, using negative feedback from the controlled pressure. Regulators are used for gases and liquids, and can be an integral device with a pressure setting, a restrictor and a sensor all in the one body, or consist of a separate pressure sensor, controller and flow valve. Two types are found: the pressure reduction regulator and the back-pressure regulator.
A pressure reducing regulator is a control valve that reduces the input pressure of a fluid to a desired value at its output. It is a normally-open valve and is installed upstream of pressure-sensitive equipment. A back-pressure regulator, back-pressure valve, pressure-sustaining valve or pressure-sustaining regulator is a control valve that maintains the set pressure at its inlet side by opening to allow flow when the inlet pressure exceeds the set value. It differs from an over-pressure relief valve in that the over-pressure valve is only intended to open when the contained pressure is excessive and is not required to keep upstream pressure constant. They differ from pressure-reducing regulators in that the pressure-reducing regulator controls downstream pressure and is insensitive to upstream pressure. It is a normally-closed valve which may be installed in parallel with sensitive equipment or after the sensitive equipment to provide an obstruction to flow and thereby maintain upstream pressure. Both types of regulator use feedback of the regulated pressure as input to the control mechanism and are commonly actuated by a spring-loaded diaphragm or piston reacting to changes in the feedback pressure to control the valve opening. In both cases, the valve should be opened only enough to maintain the set regulated pressure. The actual mechanism may be very similar in all respects except the placing of the feedback pressure tap. As in other feedback control mechanisms, the level of damping is important to achieve a balance between fast response to a change in the measured pressure and stability of output. Insufficient damping may lead to hunting oscillation of the controlled pressure, while excessive friction of moving parts may cause hysteresis.
Pressure reducing regulator
Operation A pressure-reducing regulator's primary function is to match the flow of gas through the regulator to the demand for fluid placed upon it, whilst maintaining a sufficiently constant output pressure. If the load flow decreases, then the regulator flow must decrease as well. If the load flow increases, then the regulator flow must increase in order to keep the controlled pressure from decreasing because of a shortage of fluid in the pressure system. It is desirable that the controlled pressure does not vary greatly from the set point for a wide range of flow rates, but it is also desirable that flow through the regulator is stable and the regulated pressure is not subject to excessive oscillation. A pressure regulator includes a restricting element, a loading element, and a measuring element:
The restricting element is a valve that can provide a variable restriction to the flow, such as a globe valve, butterfly valve, poppet valve, etc. The loading element is a part that can apply the needed force to the restricting element. This loading can be provided by a weight, a spring, a piston actuator, or the diaphragm actuator in combination with a spring. The measuring element functions to determine when the inlet flow is equal to the outlet flow. The diaphragm itself is often used as a measuring element; it can serve as a combined element. In the pictured single-stage regulator, a force balance is used on the diaphragm to control a poppet valve in order to regulate pressure. With no inlet pressure, the spring above the diaphragm pushes it down on the poppet valve, holding it open. Once inlet pressure is introduced, the open poppet allows flow to the diaphragm and pressure in the upper chamber increases, until the diaphragm is pushed upward against the spring, causing the poppet to reduce flow, finally stopping further increase of pressure. By adjusting the top screw, the downward pressure on the diaphragm can be increased, requiring more pressure in the upper chamber to maintain equilibrium. In this way, the outlet pressure of the regulator is controlled. This operation is described by the following equation:
F = ( P i − P o ) s + P o S + f , {\displaystyle F=(P_{\text{i}}-P_{\text{o}})s+P_{\text{o}}S+f,}
where
F {\displaystyle F} – diaphragm spring force,
f {\displaystyle f} – poppet spring force,
P i {\displaystyle P_{\text{i}}} – inlet pressure,
P o {\displaystyle P_{\text{o}}} – outlet pressure,
s {\displaystyle s} – poppet area,
S {\displaystyle S} – diaphragm area.
Single-stage regulator
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