Pressure reducing valves

By 2 June 2018

In a complex compressed air system there are likely to be several sub-systems or branch lines that need to have a pressure limitation, lower than the main pressure, placed on them. Too high a pressure can result in energy wastage, and many tools and other equipment either work best (or only) at their design pressure.

A pressure reducing valve (commonly known as a pressure regulator) is used in these circumstances. It reduces a high variable primary pressure to a lower, constant secondary pressure; it measures and corrects deviations in pressure. A regulator should also include a bleed so that if the secondary pressure exceeds the setting of the valve, the excess pressure can escape. A regulating valve must possess certain characteristics for reliable operation. The valve must be fitted with a balanced poppet valve otherwise pressure fluctuations will cause instability. The controlled pressure must be practically constant for all flow rates up to the rated maximum.

It is customary to install a combined assembly of filter regulator and lubricator (FRL) to filter out the free water droplets, then control the pressure and finally lubricate the controlled air. This assembly is used to supply regulated air to a branch of the main supply. It is usually built up in modular form and available in this form from a number of manufacturers. Not all elements of the assembly are required in every case. Thus for example if the air has already been filtered and the moisture removed, there is no need for an additional filter. A commonly available modular unit is a combined filter and regulator, the function of which is shown in Figure 6, which also includes a description of a microlubricator. A filter regulator of this kind should also incorporate a pressure gauge to assist in setting the spring pre-load. The bowls of the filter and lubricator are often made of a transparent plastic, so that a visual check can be kept on the amount of the moisture and the lubricant. A metal safety guard can be fitted to enclose the polycarbonate bowl and allmetal equipment is also available. It is better, if the installation permits it, to have an automatic drain on the filter bowl, which then allows the fitting of a safer metal bowl.

Electronically-set pressure regulators are available for remote control of the pressure.