1. What is Pressure Reducing Valve?

Pressure reducing valve, English name is Pressure Reducing Valve (abbreviated as PRV), is a valve line with the function of stabilizing the output pressure at a predetermined level, and the outlet pressure is always less than the inlet pressure. Pressure reducing valve is used for the purpose of adjusting the outlet pressure to the desired level, ensuring suitable for the operating pressure of the system behind the valve. The pressure relief valve is usually fitted with two pressure gauges, one to measure the inlet pressure, the other to measure the outlet pressure, making it easy for users to observe when operating the valve.

2. Basic structure of pressure reducing valve

Like the  construction of a safety valve  (backlink to post number 09), the pressure reducing valve also usually includes 2 types: direct pressure reducing valve and indirect pressure reducing valve.

a. Direct pressure reducing valve:  This is a commonly used valve line, with a simpler structure than an indirect pressure reducing valve line, usually including the following details:

-  Body:  It is a part usually made from copper, cast iron, steel, stainless steel, ... (depending on the characteristics of the medium & the specific requirements of the customer), the body of the valve protects and connects other parts of the valve into a unified block.

- Disc valve (Disc): As a part in direct contact with the medium, it is usually made from metals that are resistant to corrosion, good temperature & pressure, and have high hardness. The main function of the valve disc is to allow the flow to pass through the valve & the diaphragm to prevent overflow into the regulating spring, affecting the elasticity.

- Elastic spring (Adjusting screw):  Deciding directly to the pressure adjustment, it is usually made of alloys with high hardness, high strength, creating good elastic force allowing the pressure value to be adjusted. output power to the desired level most accurately.

- Adjustment knob (Cap):  Usually located on the top of the valve, directly linked to the elastic spring and is a spring tension adjustment part, thereby allowing the outlet pressure to be adjusted to the value. exactly what you want.

b. Indirect pressure reducing valve:  Indirect pressure reducing valve has a more complex structure than the direct pressure reducing valve line, often used in pipelines of large size or pressure. The specific structure of the valve includes the following main parts:

-  Body:  It is a part usually made from copper, cast iron, steel, stainless steel, ... (depending on the characteristics of the medium & the specific requirements of the customer), the body of the valve protects and connects other parts of the valve into a unified block.

- Disc valve (Disc): As a part in direct contact with the medium, it is usually made from metals that are resistant to corrosion, good temperature & pressure, and have high hardness. The main function of the valve disc is to allow the flow to pass through the valve & the diaphragm to prevent overflow into the regulating spring, affecting the elasticity.

- Elastic spring (Adjusting screw):  Deciding directly to the pressure adjustment, it is usually made of alloys with high hardness, high strength, creating good elastic force allowing the pressure value to be adjusted. output power to the desired level most accurately.

- Valve shaft (Stem):  The valve shaft is directly linked to the valve disc, has the effect of raising / lowering the valve disc, thereby allowing / preventing flow through the valve.

- Pilot valve:  usually a direct pressure reducing valve line, from here can adjust and control the pressure to help stabilize the output pressure.

- Pressure Gauge:  Usually installed at the inlet & outlet of the system, helping users better recognize & control the operating pressure & efficiency of the valve.

c. Working principle of pressure relief valve

* Direct pressure relief valve:

Direct pressure relief valve works by a simple mechanism, the flow on the pipeline when circulating to the valve inlet will be blocked, the pressure is strong enough than the elastic force of the spring will push the diaphragm and disc. valve lifts high. At this time, the fluid flow will pass with a limited degree (less than the inlet pressure) to help the following equipment operate with the most stability and efficiency.

When the inlet pressure of the valve decreases, at this time the force of the spring to overcome the flow pressure will push the valve disc down, the valve is still open with low flow through. When the pressure is increased close to the set rated pressure, it will act on the elastic membrane, push the diaphragm along the valve disc upwards, the valve is closed. The cycle repeats itself giving us the most stable valve outlet pressure.

* Indirect pressure relief valve:

When the valve is in the normal open state, the flow is allowed to pass with a pressure sufficient for the operation of the system and always less than the valve set pressure. When inlet flow is high pressure, higher than system set pressure from Pilot. Then the valve disc will rise, but not completely, but only to ensure that the outlet pressure meets the system requirements.

When the pressure exceeds the system's tolerance, we will adjust the pilot's pressure reducing screw to reduce the pressure on the outlet, thereby protecting the safety of the system.

d. Advantages & disadvantages of pressure relief valve

* Advantages:

– Pressure reducing valve usually works well, durable at high pressure and temperature.

– Made from many different material lines, suitable for installation for many diverse applications of customers.

Valves operate completely automatically, independent of any external force.

* Defect:

- Pressure relief valve is similar to the one-way valve. Therefore, the valve will be adversely affected if there is an opposite effect of the flow.

– The size of the valve to be manufactured is limited by the DN500 size, and the valve needs to be calculated correctly before production.