Working principle and product application of electric control valve

working principle

The electric control valve is used to regulate the flow, pressure and hydraulics of the medium. According to the signal of the regulating position, the opening of the valve is automatically controlled, so as to achieve the regulation of medium flow, pressure and hydraulics. The control valves are divided into electric control valves, pneumatic control valves and hydraulic control valves. The regulating valve is composed of an electric actuator or a pneumatic actuator and a regulating valve. The electric control valve is generally divided into two types: straight single seat control valve and straight double seat control valve. The latter has the characteristics of large flow capacity, small imbalance and stable operation, so it is usually especially suitable for the occasions with large flow, high pressure drop and little leakage.

The flow capacity Cv is one of the main parameters for selecting the electric control valve. The flow capacity of the control valve is defined as: when the control valve is fully open, the pressure difference at both ends of the valve is 0.1MPa, and the fluid density is 1g/cm3, the flow rate of the control valve per hour is called the flow capacity, also called the flow coefficient, expressed in Cv, and the unit is t/h. The Cv value of the liquid is calculated according to the following formula.

Installation precautions

(1) Prevent leakage

The valve shall not leak during installation. The electric control valve has been used for several years. If gaps or holes are formed in the stuffing box, flange gasket and other parts, leakage may occur. If the operating conditions of the fluid medium are very harsh, such as high temperature, high pressure and corrosive fluid, the damage will become more and more serious and the leakage will become more and more severe.

There are many ways to prevent leakage. In the installation process, the selection of packing, the selection of sealing method, the reduction of pressure, and the use of valves with good sealing are all factors considered by the installation personnel.

(2) Install vent valve or drain valve

a. Any pipeline design and installation will inevitably retain high-pressure fluid when it is cut off. If the potential energy of the accumulated fluid is very dangerous, a vent valve and/or a drain valve shall be installed on each side of the electric control valve.

b. For valves with large amount of high-pressure materials accumulated, two vent valves or drain valves shall be considered. In this way, only a small amount of material is accumulated between the two valves, and the system pressure can be released one by one. During this process, the electric control valve is opened.

c. A large amount of high-pressure fluid accumulated between the shut-off valves may accumulate considerable force. If the operation of releasing the pressure of the electric control valve is careless, serious personal accidents may occur. After the system is cut off, the system pressure in the valve can be maintained for a period of time. If the valve is to be repaired and opened or removed at this time, there are safety measures to reduce the pressure, as well as measures to discharge the accumulated harmful fluid.

d. A vent valve capable of limiting flow shall be selected to protect operators. If the fluid contains suspended particles, it is easy to block the vent valve. Therefore, in order to vent safely, the vent valve installed on the top of the pipe shall be a large size vent valve.

(3) Safe pipeline

a. Sand, scale, metal chips and other impurities in the pipeline will damage the surface of the electric control valve, making it not closed tightly. Therefore, before installing the electric control valve, all installed pipelines and pipe fittings should be purged and purified.

b. If the discharged fluid is dangerous gas, the vent pipeline shall be connected to a safe place. Even nonflammable gas should still be led out by vent pipe to avoid injury to operators due to rust or other sundries carried by the blown gas. If the discharged fluid is dangerous liquid, consider connecting the discharge pipe to a safe container. During operation, the valve may be very hot, and precautions are taken to prevent operators from being scalded.

c. When installing threaded pipe fittings, avoid sealant falling into the installation pipe. Therefore, the sealant shall be used as little as possible, and the first two threads shall not be coated with sealing material. PTFE sealing strip can be used instead of sealant for sealing.

d. Steam management upstream or downstream of the electric control valve shall be insulated.

e. In piping systems with severe pressure fluctuations, pipe buffers are recommended.