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A pressure reducing valve (PRV) is designed to reduce and maintain a stable outlet downstream pressure regardless of upstream or inlet pressure changes to protect downstream equipment from over pressure damage. Many process applications will have pressure changes due to pump activity, other control valve movements and system flow demands elsewhere upstream and because of this the system pressure can vary significantly.
The pressure reducing valve will remain open allowing the flow of liquid or gas media downstream, but if the outlet pressure increases close to the pre-set limit the pressure reducing valve will begin to close to regulate and maintain a stable outlet pressure. When the outlet pressure drops below the safe limit the pressure reducing or regulating valve will slowly open again allowing flow and thus increasing the outlet pressure according to the valve pressure setting.
PRV valves can be manually adjusted within their set limits with the outlet pressure being displayed by an external pressure gauge.
Pressure regulating control valves are available across a wide range of adjustable pressure settings such as 25 to 1 bar, 10 to 0.2 bar, 12 to 1 bar and 5 to 0.02 bar, and all can be manually adjusted within these pressure ranges to suit each application, with custom pressure ranges available.
Pressure reducing valves also known as pressure regulating valves or pressure control valves are available with either threaded or flanged port connections ranging from 1/2", 3/4", 1", 11/2" and 2" BSP or NPT thread or DN15, DN20, DN25, DN40, DN50, DN65, DN80, DN100, DN125, DN150, DN200, DN250, DN300, DN350, DN400, DN450, DN500 up to DN1000 PN16 or ANSI150lb flange.
Pressure reducing valves (PRV's) are typically available in 316 or 304 stainless steel, brass, bronze, cast iron or ductile iron with epoxy coatings. Most pressure reducing valves are designed for process water systems, with the PRV valve material chosen according to the application at hand. Most general purpose water systems will use a more cost friendly ductile iron or brass PRV, however applications in the food processing, beverage or chemical processing industries would prefer stainless steel, as there could be aggressive or corrosive cleaning chemicals present within the environment.
Like many valve products the pressure regulating valve has evolved to meet the specific requirements for each industrial application and process system that use them. The most popular variants are:
A direct acting 316 stainless steel pressure reducing valve (PRV) offers direct system pressure control and pressure reducing protection without the need for guaranteed pressure differences, making them ideally suited to closed loop or closed end systems where constant flow is not guaranteed. Typically a very robust design with fully adjustable pressure reducing settings anywhere between 25 bar down to 1 bar depending on model or manufacturer my means of a knob, handle or bolt located at either the base or top of the valve body with the reduced outlet or downstream pressure displayed by a pressure gauge.
A direct acting low pressure reducing valve PRV offers the same direct acting system pressure control and pressure reduction but with a larger pressure balanced diaphragm offering improved low pressure sensitivity. These low pressure PRV's are ideally suited for reducing and maintaining stable reduced and controlled outlet pressures for most low pressure applications between about 0.2 bar up to 1.5 bar depending on make and model of choice. The outlet pressure is easy to adjust by means of a T bar or bolt mounted either above or below the main valve body, turning this will either increase or reduce the outlet pressure which can be monitored by a pressure gauge which is typically included with most low pressure PRV's.
A direct acting micro pressure pressure reducing valve (PRV) offer the same direct acting functionality as most other PRV's, except in this case the pressure control diaphragm is much larger offering extremely sensitive pressure control. These micro pressure PRV are ideally suited for reducing and maintaining very stable and precise outlet pressures for very low pressure applications typically between 0.02 bar (0.3 psi) up to 0.2 bar (3 psi), and can me manually adjusted via a locking nut or T bar protruding from either the top or lower valve body perpendicular to the valve ports. The outlet pressure of a micro PRV will be displayed by a pressure gauge typically mounted directly into the valve body.
A pressure operated or pilot assisted pressure reducing valve (PRV) utilises then pressure difference between the inlet (upstream) and outlet (downstream) to control the valve function via an externally mounted and typically small external PRV controller. As pilot operated valves are typically larger in size i.e. upwards from 50mm, there is a guarantee of pressure difference. This design of external control pressure control system greatly reduces cost compared to large bore direct acting PRV's, and the external controllers can be removed and replaced to aid shipping, handling, installation and maintenance processes. Typical pressure reducing ranges from about 1 bar (15 psi) up to about 12 bar (180 psi), with pressure adjustment via the external controller turn screw or T bar handle and the current reduced outlet pressure displayed by an external pressure gauge.
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