Difference between Pilot-operated & Self-compensating  pressure regulators

Introduction

Gases used in industrial processing, such as oxygen, nitrogen, hydrogen, and propane, are stored in high-pressure containers in liquid form. The high-pressure gases from above the liquid are reduced in pressure and regulated with gas regulators to a lower pound per square inch before they can be distributed through the facility. The gas lines may have additional regulators at the point of use.We are gonna discuss about such Pressure regulators in this session

Self-compensating pressure regulators

A spring-controlled regulator is an internally controlled pressure regulator and is shown in Fig below. Initially, the spring holds the inlet valve open and gas under pressure flows into the main cylinder at a rate higher than it can exit the cylinder. As the pressure in the cylinder increases, a predetermined pressure is reached where the spring loaded diaphragm starts to move up, causing the valve to partially close, i.e., the pressure on the diaphragm controls the flow of gas into the cylinder to maintain a constant pressure in the main cylinder and at the output, regardless of the flow rate (ideally). The output pressure can be adjusted by the spring screw adjustment. A weight-controlled regulator is shown in Fig below. The internally controlled regulator has a weight-loaded diaphragm. The operation is the same as the spring-loaded diaphragm except the spring is replaced with a weight. The pressure can be adjusted by the position of a sliding weight on a cantilever arm.

Self-compensating pressure regulators (a) spring loaded and (b) weight loaded.                        Self-compensating pressure regulators (a) spring loaded and (b) weight loaded.

A pressure-controlled diaphragm regulator is shown in Fig below. The internally controlled regulator has a pressure-loaded diaphragm. Pressure from a Regulated external air or gas supply is used to load the diaphragm via a restriction. The pressure to the regulator can then be adjusted by an adjustable bleed valve, which in turn is used to set the output pressure of the regulator. Externally connected spring diaphragm regulator is shown in Fig below. The cross section shows an externally connected spring-loaded pressure regulator. The spring holds the valve open until the output pressure, which is fed to the upper surface of the diaphragm, overcomes the force of the spring on the diaphragm, and starts to close the valve, hence regulating the output pressure. Note that the valve is inverted from the internal regulator and the internal pressure is isolated from the lower side of the diaphragm. Weight- and air-loaded diaphragms are also available for externally connected regulators.

 Self-compensating pressure regulators (a) internal pressure-loaded regulator and (b) externally connected spring-loaded regulator.

 Self-compensating pressure regulators (a) internal pressure-loaded regulator and (b) externally connected spring-loaded regulator.

Pilot-operated pressure regulators

Pilot-operated pressure regulators can use an internal or external pilot for feedback signal amplification and control. The pilot is a small regulator positioned between the pressure connection to the regulator and the loading pressure on the diaphragm. Figure below shows such an externally connected pilot regulator. The pressure from the output of the regulator is used to control the pilot, which

 

 

(a) a pilot-operated regulator and (b) an automatic pressure safety valve.

(a) a pilot-operated regulator and (b) an automatic pressure safety valve.

 

In turn amplifies the signal and controls the pressure from the air supply to the diaphragm, giving greater control than that available with the internal pressure control diaphragm. A slight change in the output pressure is required to produce a full pressure range change of the regulator giving a high gain system for good output pressure regulation. An Instrument pilot-operated pressure regulator is similar to the pilot-operated pressure regulator but has a proportional band adjustment included, giving an gain or sensitivity control feature to provide greater flexibility in control.

Advantages of Piloted Regulators

  • More accurate
  • Less drop
  • More sensitive – Small change in pilot = large change in main valve
  • Higher range ability

Disadvantages of piloted regulators

  • More sensitive – Can create oscillations with in a system
  • Not good for rapidly changing system

Also read about different types of pressure measurement techniques

https://automationforum.co/category/pressure-measurement

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