In the gas industry, there are two basic types of regulators used for both pressure reducing and back pressure (relief) control. The two types are:
• Self Operated Regulators
(Sometimes referred to as spring loaded regulators)
• Pilot Operated Regulators (Loading and Unloading style pilot regulators)
This paper will discuss the basic principle of Self Operated and Pilot Operated Regulators including components of the system, principles of operation, advantages and disadvantages, and some maintenance and inspection procedures.
SELF OPERATED REGULATORS
A Self Operated Regulator consists of a spring opening valve that is directly opposed by a diaphragm assembly
Fig. 1 Self Operated Regulator
(See Figure 1). As downstream pressure increases, the diaphragm will overcome the spring force and close the valve. When downstream pressure decreases, the spring force is greater than the force of the gas acting on the diaphragm and the valve opens.
There are practical, engineering, cost, size, and performance limitations that limit the applications for self operated regulators. For application requiring high pressure drops (over 200 psig) and high outlet pressures (15 to 200 psig), orifice sizing are limited to a maximum of 1/2”, and smaller orifices are required as the pressure drop increases. These regulators fall into a category referred to as “Farm Tap Regulators”. Another group referred to as “Industrial Regulators” handle outlet pressure from inches of water column to 5 psig with orifice sizes up to 2 inches. The self operated regulator with the “Rollout Diaphragm” is an exception and is available in fairly high outlet pressures (100 psig) and up to 6 inches in size. However, in these pressure ranges and valve sizes, a Pilot Operated Regulator generally offers better accuracy and more capacity at a lower cost. Refer to the Regulator Selection Chart of Outlet Pressure versus Orifice Valve Size (See Figure 2) for a graphic indication of where Self Operated Regulators are used in the gas industry.