Classification, Characteristics, Maintenance and Repair Guidelines of Hydraulic Control Valves 

I. Classification System 

Hydraulic control valves are classified into various types through the combination of structure and function. The core classification logic is as follows: 

1. By function classification 

Water level control valve: Applied in scenarios such as water tanks and water towers, it activates the valve to open or close through a float ball or pressure sensor to maintain a stable liquid level. 

Pressure reducing valve: Reduces high-pressure fluid to the set low pressure and automatically maintains pressure stability relying on the energy of the medium. Typical applications include water supply systems for high-rise buildings. 

Safety valve: Automatically releases pressure when the system pressure exceeds the safety threshold, protecting the pipeline and equipment from damage. Commonly found in boilers and pressure vessels. 

Check valve: Prevents the backflow of the medium and eliminates the water hammer effect. It is mostly installed at the outlet of the pump. 

Flow control valve: Limits the flow rate of the fluid to a preset value, achieving the conversion from high pressure at the upstream to low pressure at the downstream. It is applicable to irrigation and industrial cooling systems. 

Pressure differential balancing valve: Maintains a constant pressure difference between the supply and return water pipes or the water collector in the air conditioning system, optimizing the efficiency of heat exchange. 

Emergency shut-off valve: In the system for both fire protection and domestic water supply, it automatically switches the water supply direction to ensure the demand for emergency water. 

Sludge discharge valve: It includes the diaphragm-type quick-opening sludge discharge valve and the diaphragm-type sludge discharge valve at the bottom of the tank, which are used for removing the sludge at the bottom of the sedimentation tank. 

2. Classified by driving method 

Self-operated: The valve operates based on the pressure difference of the medium, without the need for external energy sources such as pressure reducing valves or safety valves. 

Electric type: Using an electromagnetic valve as the trigger, it remotely controls the opening and closing of the valve through electrical signals, replacing the large-sized electric devices of traditional gate valves or butterfly valves. 

Pneumatic/Liquid-powered: Utilizing compressed air or hydraulic oil to transmit power, suitable for explosion-proof or remote control scenarios. 

3. Subdivide according to structural characteristics 

Direct-flow valve: Fluid flows in a straight line, with low resistance, suitable for low-pressure high-flow systems. 

Three-way valve: Diversion or confluence design, meeting the requirements of complex piping systems. 

Angle valve: Changes the direction of the fluid by 90°, saving installation space. 

II. Key Features 

1. Safety and reliability 

It integrates a triple water hammer elimination mechanism consisting of quick-closing, slow-closing and energy-absorbing chambers, ensuring no accidental contact risks during operation. 

Fault retention design: When an air-open valve fails, it closes; when an air-closing valve fails, it opens, or the retention valve is used to maintain the opening degree before the failure. 

2. Adaptive Control 

No manual operation required. The pump starts and stops automatically, and the valve status is adjusted according to the pressure difference of the medium. 

Strong anti-interference ability: The operation is not affected by the liquid level difference, water outlet pressure and flow fluctuations. 

3. Economy and Durability 

The water self-priming valve body does not require additional lubrication, resulting in low maintenance costs. 

The diaphragm and O-ring are vulnerable components. However, they are designed to have a long service life, and the overall valve can last for more than 10 years. 

Significant energy saving: By using imported pressure support diaphragm plates, resistance losses are reduced. 

4. Trend of Structural Optimization 

Compact actuators: Reduce costs and enhance throughput capacity. 

Sleeve guidance: Reduces friction and noise, improves interchangeability of flow characteristics. 

Balanced valve core: Reduces the thrust of the actuator and optimizes the dynamic performance of the system. 

Integrated valve core/valve seat: Designed with the same material, this ensures a reduction in leakage and imbalance forces. 

III. Maintenance Process 

1. Preparations before the event 

Close the front and rear gate valves of the main valve to cut off the fluid supply. 

Loosen the screw of the pipe connection on the main valve cover to release the residual pressure inside the valve. 

2. Disassembly and Inspection 

Remove all the screws, including the nuts on the copper pipes of the control pipeline. 

Remove the valve cover, spring, shaft core, diaphragm and piston. Be careful not to damage the diaphragm. 

Check the diaphragm and O-ring: If there are cracks, deformations or aging, new parts need to be replaced. 

Clean the interior of the main valve: Remove debris and deposits from the valve seat, shaft core, and other parts. 

3. Reassembly 

Install the components in reverse order to ensure that the valve operates smoothly without any obstruction. 

After maintenance, install it horizontally and keep the valve cover facing upwards to prevent functional abnormalities caused by reverse installation. 

IV. Maintenance Points 

1. Replacement of vulnerable parts 

The diaphragm and O-ring are high-frequency replacement parts, and it is necessary to select products that match the original factory specifications. 

When the shaft core nut becomes loose, the diaphragm or O-ring should be disassembled step by step to avoid secondary damage caused by forced removal. 

2. Fault Diagnosis 

Valve jamming: Check the gap between the valve seat and the shaft core, remove foreign objects or adjust the mating tolerance. 

Excessive leakage: Confirm the integrity of the diaphragm, and check if the valve seat sealing surface is worn. 

Slow movement: Check whether the medium pressure meets the standard, or clear the blockage in the control pipeline. 

3. Performance Optimization 

Regularly verify the set pressure of the safety valve to ensure it matches the safety requirements of the system. 

Carry out a pressure stabilization test on the pressure reducing valve and adjust the parameters of the pilot valve to maintain a stable outlet pressure. 

Install a filter in front of the flow control valve to prevent impurities from entering the valve chamber and affecting its accuracy.