Maintaining control in pressure-related industrial applications is important to the success of an operation in terms of both performance and safety. A pressure regulator is a self-contained mechanical control device that usually does not rely on any external power sources. This device employs a sensor, valve, and controller unit. Although the two are similar, it is important to make the distinction between a regulator and a control valve. Regulators tend to be less expensive and relatively easier to install and maintain. However, applications requiring larger valve sizes may be better served by control valve systems.
When working with compressed gas in cylinders or other containers, pressure regulators are vital for maintaining proper gas discharge. These regulators are employed for controlling both liquefied and non-liquefied gas forms. While there are numerous types of different gas regulators, most devices are selected based on their range of delivery pressures, their level of accuracy, the quality of their design and construction materials, and the flow rate involved in the project.
Gas Pressure Regulator Design
A standard compressed gas pressure regulator incorporates a gas-loaded or spring-loaded diaphragm mechanism that regulates the opening and closing of a gas discharge orifice. This mechanism can be calibrated manually to provide constant delivery pressure at any value within a designated range. After the desired delivery pressure is set, the regulator opens or closes the gas discharge to maintain constant pressure. Gauges are often attached to the regulator system to provide readings on the pressure levels and valves are used to control the volume of gas flow.
Types of Gas Pressure Regulators
Most pressure regulators are either single-stage or two-stage devices. As gas cylinder pressure decreases, single-stage regulators produce minor fluctuations in delivery pressure, and delivery pressure also declines as the flow rate rises. In contrast, a two-stage regulator provides a more constant pressure level under a range of diverse operating conditions. This is due to the two-step process between cylinder pressure reduction and delivery pressure, which lowers the effect of delivery pressure fluctuations on regulator operations. The potential for lockup, which is the pressure increase beyond the delivery point that can cause flow to cease, is also higher for single-stage regulators than it is for their two-stage counterparts.
Controlling Gas Pressure
In order to safely discharge non-liquefied gases, cylinder pressure must be carefully reduced using pressure regulators. The compression within the gas container may be as high as several thousand psig (pound-force per square inch), while the pressure level during actual gas usage is often considerably lower. Liquefied gas can be held within a container in both liquid and gaseous forms at a pressure level equal to that of the gas’s vapor pressure. Cylinder pressure will correspond to that of vapor pressure as long as liquid is held within the cylinder and once all the liquid is discharged the cylinder pressure will drop. Single-stage regulators are effective in maintaining constant pressure while liquid remains in the container, but a two-stage regulator is necessary for discharging all of the material.
When handling material in a gaseous state, discharging too rapidly can cause liquid elements in the container to cool very quickly, dropping the pressure and flow rate below operating parameters. Specialized liquid flow regulators or manual control valves are often used to release this liquid phase of the gas at vapor pressure, preventing any sudden pressure drops. Likewise, pressure relief devices can be employed to prevent excess pressure buildup, which can be caused by blockage of the gas line.
For more information on the physics behind general pressure regulators, see Cheresources.com.
Gas Pressure Regulator Installation and Use
Installing a pressure regulator on a gas cylinder requires certain precautions, and manufacturers’ recommendations should always be consulted before any setup process. If the threads do not engage, the regulator may be incompatible for that type of gas cylinder and should not be forced into fitting. Some suggestions that may help in achieving the necessary delivery pressure include:
• Rotation: Once a regulator has been attached to a cylinder outlet, it may help to rotate the delivery pressure screw counterclockwise so that it turns more easily.
• Valve Opening: The cylinder valve can be gradually opened until the tank gauge begins providing pressure readings. This pressure can be checked to determine if it meets project requirements. If it doesn’t, a malfunction or leak check can help to identify the problem.
• Flow-Control: When the flow-control valve is closed, turning the delivery pressure screw clockwise can help to achieve the needed delivery pressure. The regulator’s flow-control valve can then be used to maintain the necessary flow levels.
Other Instruments & Controls Guides