There is no pressure behind the valve – is it a problem with the valve or with the pipeline design?
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Medium: High-temperature water; main pipeline pressure is 12 Mpa. The high-pressure stop valve features a design with high inlet and low outlet. The original design involved creating a bypass pipeline at the opening of the main pipeline, with this bypass pipeline consisting of an inlet stop valve, a pressure reducing valve, and an outlet stop valve (see diagram). When the bypass stop valve is not opened, the pressure at the end of the bypass pipeline is 4 MPa. (The pressure reducing valve has not been calibrated yet.) Now, open the valve on the main pipeline and then open the inlet stop valve of the bypass. The pressure gauge behind the pressure reducing valve does not show any pressure, and fluid is flowing out from the drain valve below; the flow rate of water is not high. There is no pressure gauge installed at the inlet of the customer’s pipeline bypass, so it is unknown what the inlet pressure is. Due to the pressure in the main pipeline, fluid is flowing into the bypass pipeline; as a result, the pressure gauge behind the valve does not show any pressure. The customer suspects that the valve core of the inlet stop valve may have fallen out, preventing fluid flow (the valve stem can move up and down normally). I think now that there might be an issue with the pipeline design, which is causing no pressure in the bypass pipeline.
It can’t be, is there a problem with the pressure relief valve?
Since there was no pressure in front of the pressure reducing valve, it could not be properly calibrated; as a result, it was impossible to determine whether there was a problem with the valve
It is likely that there is a fault with the pressure reducing valve; maybe the pressure sensing wire of the valve is installed in the wrong direction.
Over 80% are cases of the valve disc falling off in globe valves
It is now confirmed that the valve disc of the stop valve has not fallen off
If it is to control the pressure behind the valve, a pressure tap is installed behind the valve; the valve closes when the pressure exceeds the set value and opens when the pressure drops； When controlling the pressure in front of a control valve and a pressure tap is installed in front of the valve, it mainly depends on whether you are controlling the pressure in front of or behind the valve.
This post was last edited by jfwzf on 2017-9-5 15:23. Clogged with slag?
This post was last edited by jfwzf on 2017-9-5 at 15:21. 1. A pressure relief valve reduces the inlet pressure to a desired outlet pressure by throttling through a control element, thereby maintaining a stable outlet pressure. When the pressure relief valve leaves the factory, the adjusting spring is in an uncompressed state; at this time, both the main valve disc and the auxiliary valve disc are closed. During use, the adjusting screw is turned clockwise to compress the adjusting spring, which causes the diaphragm disc to move upward and push open the auxiliary valve disc. The fluid then passes from hole A, through the auxiliary valve seat, to hole B and enters above the piston. Under the pressure of the fluid, the piston moves downward, pushing the main valve disc away from the main valve seat and allowing the fluid to flow behind the valve. At the same time, fluid enters beneath the diaphragm through port c; when the pressure behind the valve exceeds the set pressure, this force pushes the diaphragm upward, compressing the adjustment spring. As a result, the secondary valve flap moves in the direction of closure, reducing the flow of fluid above the piston and thereby lowering the pressure. At this point, the main valve flap moves up and down under the force of the spring attached to it, narrowing the gap between the main valve flap and the main valve seat. This leads to a reduction in the flow rate of fluid, and the pressure behind the valve drops to a new equilibrium. Conversely, when the pressure behind the valve is below the set pressure, the gap between the main valve flap and the main valve seat widens, resulting in an increase in the flow rate of fluid and an increase in the pressure behind the valve, until a new equilibrium is reached. 2 What adjustments have been made to the pressure relief valve?