Hydraulic control valve

Hydraulic control valves are a general term for a series of multi-purpose control and safety valves. It mainly includes: 1: Remote-controlled float valve ； 2: Pressure relief valve ； 3: Slow-closing check valve ； 4: Pressure relief valve ； 5: Pressure-holding valves, etc. Their main features are: they operate by utilizing the pressure of the medium itself and a hydraulic system, allow for automatic control, offer precise performance and reliable reliability, and can be widely used in pipelines of domestic, industrial, and fire-fighting water supply systems to serve control and safety purposes. This post was last edited by hyypw on 2008-1-18 18:53]

The basic principle is that when the main valve is closed, liquid is injected through the water-injection valve located at the upper part of the valve body; thereafter, the water-outlet valve at the lower part of the valve body is opened. If the injection of water and the discharge of water occur simultaneously, it indicates that the valve is tightly closed. Otherwise, the water injected will flow into the pipeline through the gaps in the main valve, resulting in a decrease in the amount of water discharged from the outlet valve, or even no water being discharged at all. This type of valve allows for a relatively straightforward detection of whether the valve is closed.

The multi-functional control valves, safety pressure relief valves, and pressure regulating valves used in water systems all appear similar in appearance; what are the differences between them? What is the working principle then?

That's absolutely true. The basic valves are diaphragm valves; the difference lies in the way the connecting pipes between the two chambers are arranged, which enables various functions to be achieved. You can go to websites like “Shanghai Guanlong” and “Zhuzhou Nanfang” to check out the structural diagrams; it would be even better if you can find animated diagrams. It’s also mentioned in many valve manuals, and it’s easy to understand at a glance. The structure is simple and the design is clever; it can indeed save a lot of manual labor. They are collectively referred to as \"hydraulic control valves\", and seem to be named 100X, 200X, 300X. This post was last edited by eastone on 2008-10-22 08:46]

A hydraulic control valve is a valve that is controlled by water pressure; it consists of a main valve along with associated components such as ducts, pilot valves, needle valves, ball valves, and pressure gauges. Depending on the purpose of use, functions, and application location, it can evolve into remote-controlled float valves, pressure reducing valves, slow-closing check valves, flow control valves, pressure relief valves, hydroelectric control valves, and more. Hydraulic control valves are divided into diaphragm type and piston type; they operate on the same principle. Both use the pressure difference ΔP between the upstream and downstream sides as driving force, and are controlled by a pilot valve to enable hydraulic differential operation of the diaphragm (piston). This process is entirely automated via hydraulic means, allowing the main valve disc to open completely, close completely, or remain in a regulated state. When the pressurized water in the control chamber above the diaphragm (piston) is discharged to the atmosphere or a lower-pressure area downstream, the pressure acting on the bottom of the valve disc and below the diaphragm becomes greater than the pressure above, thereby pushing the main valve disc to its fully open position ； When the pressurized water in the control chamber above the diaphragm (piston) cannot be discharged to the atmosphere or to a lower-pressure area downstream, the pressure acting on the upper side of the diaphragm (piston) becomes greater than the pressure on the lower side; as a result, the valve disc of the main valve is pushed to a fully closed position ； When the pressure level in the control chamber above the diaphragm (piston) is between the inlet pressure and the outlet pressure, the main valve disc is in a regulating state, and its position of regulation is determined by the combined control action of the needle valve and the adjustable guide valve in the conduit system. The adjustable pilot valve can utilize the downstream outlet pressure and open or close its own small valve orifice in response to changes in that pressure, thereby altering the pressure level in the control chamber above the diaphragm (piston) and controlling the adjustment position of the main valve disc. Working principle of the pressure relief valve: 1. As a pressure relief valve: When the pressure relief/pressure holding pilot valve is set to the pressure relief mode, water flows from the needle valve, the main valve control chamber, ball valve A, the pressure relief/pressure holding pilot valve, and ball valve B to the outlet; at this time, the main valve is in the open state. When the inlet pressure exceeds the safety value set by the pressure relief/holding valve, the pressure relief valve opens automatically, releasing some water through ball valve C to relieve pressure in the pipeline. When the pressure returns to a safe level, the pressure relief valve closes automatically. When used as pressure relief valves, the ball valves are normally open. 2. As a pressure-holding valve: When the pressure-relief/pressure-holding pilot valve is set to the pressure-holding mode, the pilot valve closes as long as the water pressure at the inlet of the main valve is below the set value of the pilot valve. Boost in the main control room, main valve closed. When the water supply pressure upstream of the main valve exceeds the set pressure of the pilot valve, the pressure-retaining pilot valve opens, allowing the water in the control chamber to be discharged to the outlet through a ball valve. This reduces the pressure in the control chamber, causing the main valve to open and water supply to begin, thereby maintaining the upstream water pressure. When used as a pressure holding valve, ball valve C is kept closed or replaced with a plug.