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Regulator Selection, Installation and Operation
Introduction
The primary function of a regulator is to reduce high pressure gas in a cylinder or process line to a lower usable level as it passes from the cylinder to a piece of equipment. A regulator is not a flow control device. It is used to control delivery pressure only.
Since there are numerous hazards associated with special gases - hazards that vary with the gas, the equipment used and with the particular operation - it is necessary to take the proper precautions to assure safety in high-pressure gas control. Before performing any operation with which you are not familiar, seek the advice of an experienced individual. In addition to adhering to the safety and operating rules, the user should be aware of the additional safe operating practices peculiar to each piece of equipment and each application. Particular care should be taken in the selection of equipment for use with highly oxidising gases such as oxygen and fluorine (where special cleaning, degreasing and drying is required), highly reactive gases like fluorine (where special passivation is required) and acetylene (where the use of certain types of brass is prohibited). Consult Air Products Special Gases Group or your local Air Products sales office when in doubt about correct handling procedures.
Note: Never use any regulator for gases other than those for which it is intended
The following is applicable to pressure regulators used with flammable, oxidant, corrosive, inert or toxic gases, when it is necessary to reduce cylinder supply pressure to a lower pressure.
How regulators work
1. Single-stage regulators
High pressure media enters the regulator through the inlet into high-pressure chamber. When the adjusting knob is turned clockwise, it compresses the range spring and exerts a force on the diaphragm, which pushes the valve stem open. This releases gas into the low-pressure chamber, exerting an opposing force on the diaphragm. An equilibrium is reached when the spring force on the diaphragm is equal to the opposing force of the gas in the low-pressure chamber.
In a single-stage regulator, delivery pressure increases as cylinder pressure decays, because there is less gas pressure exerted on the valve stem. Thus, frequent adjustment of the control knob is required to maintain a constant delivery pressure. This does not pose a problem, however, with pipelines and liquefied gas products where inlet pressure is maintained relatively constant. For application requiring a constant outlet pressure, a two-stage regulator is recommended.
2. Two-stage regulators
A two-stage regulator functions similar to two single-stage regulators in series. The first stage reduces the inlet pressure to a pre-set intermediate pressure, typically to 300 to 500 psig (20 to 30 bar.g). By adjusting the control knob the second stage reduces the intermediate pressure to the desired delivery pressure.
Like the single-stage regulator, outlet pressure from the first stage of the two-stage regulator rises as cylinder pressure decreases. However, instead of passing out of the regulator, the gas flows into the second stage where the pressure is moderated. Thus, delivery pressure remains constant evenas the cylinder pressure decays, eliminating the need for frequent control knob adjustment.
Regulator selection, installation and operation are introduced in this article.
Keywords
Regulator
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