Self-acting valve

Those who manufacture valves are generally able to produce stand-alone valves, such as Samson, Fisher, Koso, and so on.

Fisher is good; most of the equipment used in our factory is from Fisher, and we’ve never encountered any problems with it. In fact, some domestic manufacturers also produce high-quality products, such as those from Wuzhong and SHI.

Our company uses FISHER models; we have nearly 30 units of them, and they’ve been in use for 4 years now. The quality is quite stable. Once the set values are configured at the time of initial operation, there’s basically no need to worry about them anymore. One unit was having problems; upon inspection, it was found that weld slag was trapped inside the valve, rather than being a quality issue with the valve itself. The price is likely to be much higher than that of domestic products.

I also know that FISHET is good, but the price is too high. I was wondering if there are any valves that offer good value for money?

Self-acting pressure control valve Self-acting pressure control valve Working principle of self-acting control valves 1. Working principle of self-acting pressure control valves (pressure control behind the valve) The pressure P1 of the working medium before the valve is reduced through throttling by the valve core and seat, resulting in the pressure P2 behind the valve. P2 is delivered through control lines to the lower diaphragm chamber of the actuator, acting on the top plate; the force generated thereby balances the reaction force of the spring, which in turn determines the relative position of the valve core and the valve seat and controls the pressure behind the valve. As the pressure behind the valve, P2, increases, the force exerted by P2 on the top plate also increases. At this point, the force exerted by the top plate is greater than the reaction force of the spring, causing the valve core to move toward the valve seat until the force from the top plate and the reaction force of the spring are in balance. At this point, the flow area between the valve core and the valve seat decreases, the flow resistance increases, thereby reducing P2 to the set value. Similarly, when the pressure P2 behind the valve decreases, the direction of action is opposite to that described above; this is the working principle of a self-acting (pressure behind the valve) pressure control valve. 　　2. Working principle of the self-acting pressure control valve (pressure control before the valve) The pressure P1 of the working medium before the valve is reduced through throttling by the valve core and seat, resulting in the pressure P2 after the valve. At the same time, P1 is delivered through control lines to the upper diaphragm chamber of the actuator, acting on the top plate; the force generated thereby balances the reaction force of the spring, determining the relative position of the valve core and the valve seat and thus controlling the pressure in front of the valve. As the pressure behind the valve, P1, increases, the force exerted by P1 on the top plate also increases. At this point, the force exerted by the top plate is greater than the reaction force of the spring, causing the valve core to move away from the valve seat until the force from the top plate balances the reaction force of the spring. At this point, the flow area between the valve core and the valve seat increases, the flow resistance decreases, thereby reducing P1 to the set value. Similarly, when the pressure behind the valve P1 decreases, the direction of action is opposite to that described above; this is the working principle of a self-acting (pre-valve) pressure control valve. 　　3. Working principle of the self-acting temperature control valve (heating type) The temperature control valve operates based on the principles of the incompressibility of liquids and thermal expansion and contraction. 　　It is a self-acting temperature control valve for heating; when the temperature of the object being controlled is below the set temperature, the liquid inside the thermosensitive bulb contracts, which reduces the force acting on the actuator rod. Under the influence of the spring force, the valve element opens, increasing the flow rate of heating media such as steam and hot oil, thereby raising the temperature of the object being controlled. Once the temperature reaches the set value, the valve closes. After it closes, the temperature of the object being controlled drops, and the valve opens again, allowing the heating media to flow back into the heat exchanger and raise the temperature once more, thus maintaining a constant temperature for the object being controlled. The valve opening degree is related to the difference between the actual temperature of the controlled object and the set temperature. 　　4. Working principle of self-acting temperature control valves (cooling type) The working principle of self-acting temperature control valves used for cooling can be similar to that of those used for heating; the only difference is that the valve element opens and closes under the action of the actuator and spring force, in contrast to temperature rise valves. A cold medium flows through the valve body, and these valves are primarily used for temperature control in cooling systems. 　　5. Working principle of the self-acting flow control valve: When the medium to be controlled enters the valve, the pressure P1 before the valve is transmitted to the lower diaphragm chamber through the control line. The pressure Ps, after passing through a throttle valve, is sent to the upper diaphragm chamber. The difference between P1 and Ps, namely △Ps = P1 – Ps, is referred to as the effective pressure. The difference between the thrust generated by P1 on the diaphragm and the thrust generated by Ps on the diaphragm, balanced against the spring force, determines the relative position of the valve core and the valve seat, thereby determining the flow rate through the valve. As the flow rate passing through the valve increases, that is, as △Ps increases, P1 and Ps act on the lower and upper diaphragm chambers respectively, causing the valve core to move toward the valve seat. This changes the flow area between the valve core and the valve seat, resulting in an increase in Ps. The thrust exerted by the increased Ps on the diaphragm, combined with the spring force, balances the thrust exerted by P1 on the diaphragm at the new position, thereby achieving control over the flow rate.

Fisher is the preferred choice, right?