Working principle of pressure reducing valve | Classification and function of pressure reducing valve

Do you know what a Pressure Relief Valve is? It is a special device that automatically reduces the working pressure of the pipeline. It can reduce the pressure of the higher pressure medium to a given pressure after a given pressure reduction range. It is widely used in high-rise buildings, urban water supply networks, areas with high water pressure, mines and other occasions to ensure proper service water pressure and flow at each water point in the water supply system. Let's take a look at it with Xiaobian.

The Pressure Reducing Valve works:

The pressure reducing valve is a valve that adjusts the inlet pressure to a certain required outlet pressure and relies on the energy of the medium itself to automatically maintain the outlet pressure. From the point of view of fluid mechanics, the pressure reducing valve is a throttling element whose local resistance can be changed, that is, by changing the throttling area, the flow velocity and the kinetic energy of the fluid are changed, resulting in different pressure loss, thereby achieving the purpose of decompression.

The pressure reducing valve adopts the opening degree of the opening and closing member in the control valve body to adjust the flow rate of the medium, reduces the pressure of the medium, and adjusts the opening degree of the opening and closing member by the action of the pressure behind the valve, so that the pressure behind the valve is maintained within a certain range. Inside, the cooling water is sprayed into the valve body or behind the valve to lower the temperature of the medium. This type of valve is called a decompression and desuperheating valve.

1. When there is water after the pressure reducing valve, water will generate pressure loss through the valve core. The pressure loss is determined by the size of the spool opening, and the size of the spool opening is determined by the spring force. Therefore, by adjusting the top spring of the inlet pressure reducing valve. Control the spool opening to control the pressure loss to achieve the desired post-valve pressure.

2. When there is no water after the pressure reducing valve, the pressure behind the valve increases. At this time, the pressure behind the valve is greater than the spring force before the valve is pressed. The pressure reducing valve is in a normally open state. At this time, the pre-valve fluid and the post-valve fluid are completely separated. At this time, the pressure at the outlet of the pressure reducing valve is greater than the set value, but due to the inertia, the diaphragm moving upward does not stop at once and will continue to move upward. At one point, the valve chamber at the outlet becomes larger, the volume becomes larger, and the pressure of the internal liquid drops until it is exactly equal to the set pressure value at the outlet of the pressure reducing valve.

Classification of pressure reducing VALVES:

Classified by control method: manual, electronic control, hydraulic control;

Classified by function: flow valve (throttle valve, speed control valve, split manifold), pressure valve (relieving valve, pressure reducing valve, sequence valve, unloading valve), directional valve (electromagnetic reversing valve, manual change) Directional valve, check valve, hydraulic control check valve);

According to the installation method: plate valve, tube valve, stack valve, threaded cartridge valve, cover valve;

According to the control method: manual valve, motor valve, electric valve, Hydraulic Valve, electrohydraulic valve, etc.

1. Active pressure reducing valve. The simplest pressure reducing valve, direct acting pressure reducing valve with flat diaphragm or bellows. Because the relief valve is a separate structure, there is no need to install an external sensing line downstream. The pressure reducing valve is the smallest and most economical of the three types of pressure reducing valves, designed for medium and low flow. The accuracy of the direct acting pressure reducing valve is typically +/- 10% of the downstream set point.

2. Membrane pressure reducing valve. In this type of pressure reducing valve, the double diaphragm replaces the piston in the internal pressure reducing valve. The increased diaphragm area of the pressure relief valve opens the larger main valve and has a larger capacity than the internal pilot piston relief valve at the same pipe size. In addition, the diaphragm of the pressure relief valve is more sensitive to pressure changes with an accuracy of +/- 1%. The higher accuracy is due to the positioning of the downstream sensing line (the outside of the valve), where the gas or liquid is less turbulent. The pressure relief valve is very flexible and can be used with different types of pressure reducing valve pilot valves (eg pressure valves, temperature valves, air loading valves, solenoid valves or several valves).

3. Piston pressure reducing valve. This type of pressure reducing valve integrates two types of valves - pilot valve and main valve - in one. The design of the pilot valve is similar to that of a direct acting pressure reducing valve. Exhaust pressure from the pilot valve acts on the piston causing the piston to open the main valve. This design uses the inlet pressure to open the main valve if the main valve is large and cannot be opened directly. Therefore, this type of pressure reducing valve has a higher capacity and accuracy (+/- 5%) at the same pipe size compared to a direct acting pressure reducing valve. The same as the direct-acting pressure reducing valve, the pressure inside the pressure reducing valve senses that there is no need to externally install the sensing wire.

The role of the pressure reducing valve:

1. Automatically reduce the higher gas (steam) pressure to the required low gas (steam) pressure;

2. When the gas (steam) pressure on the high pressure side fluctuates, it can automatically adjust to make the low pressure: side gas (steam) pressure stable.