The gate is a headstock ram, and motion direction of valve disc is perpendicular to the direction of the fluid, and valve can only be fully open and fully closed, can not be adjusted and the throttle. The gate valve is sealed through the valve seat and the valve disc, usually the sealing surface will surmount the metal material to increase the wear resistance, such as surfacing 1Cr13, STL6, stainless steel and so on.The disc has a rigid disc and an elastic disc. According to the difference of the disc, the gate valves are divided into rigid gate valves and elastic gate valves.
the pressure test method of gate valve
First, the disc is opened, so that the pressure inside the valve rises to the specified value. Then, close the ram, immediately remove the gate valve, check whether there is leakage on the two sides of the disc, or directly enter the test medium to the specified value on the plug of the valve cover, and check the seal on both sides of the disc. The above method is called the middle test pressure. This method is not suitable for the seal test of the gate valve under the nominal diameter of DN32mm.
Another way is to open the disc to make the valve test pressure rise to the specified value; then turn off the disc, open the blind plate at one end, and check the leakage of the seal face. Then reverse, repeat the test until qualified as above.
The sealing test at the filling and gasket of the pneumatic valve should be carried out before the seal test of the disc.
Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they cost less than other valve design, and are lighter weight so they need less support. The disc is positioned in the center of the pipe. A rod passes through the disc to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow, so it induces a pressure drop, even when open.
A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the fluid. The valve may also be opened incrementally to throttle flow.
There are different kinds of butterfly valves, each adapted for different pressures and different usage. The zero-offset butterfly valve, which uses the flexibility of rubber, has the lowest pressure rating. The high-performance double offset butterfly valve, used in slightly higher-pressure systems, is offset from the centre line of the disc seat and body seal (offset one), and the centre line of the bore (offset two). This creates a cam action during operation to lift the seat out of the seal resulting in less friction than is created in the zero offset design and decreases its tendency to wear. The valve best suited for high-pressure systems is the triple offset butterfly valve. In this valve the disc seat contact axis is offset, which acts to virtually eliminate sliding contact between disc and seat. In the case of triple offset valves the seat is made of metal so that it can be machined such as to achieve a bubble tight shut-off when in contact with the disc.
Valves can leak for a variety of reasons, including:
- The valve is not fully closed (e.g., due to dirt, debris, or some other obstruction).
- The valve is damaged. Damage to either the seat or the seal can cause leakage.
- The valve is not designed to close 100%. Valves that are designed for precise control during throttling may not have excellent on/off capabilities.
- The valve is the wrong size for the project.
- Connection size and type
- Set pressure (psig)
- Back pressure
- Required capacity