Generally, the plastic diaphragm valve is made of UPVC CPVC PVDF PP PPH, suitable material is selected according to different media and working conditions. There are some common problems and notes in the installation and use of plastic diaphragm valve.
Plastic diaphragm valve has flange connection and socket bonding / welding connection. When install the diaphragm valve with flange connection, pay attention to keep the flange surface clean to prevent small hard objects from scratching the flange surface. Generally, rubber gasket is used. When tightening the flange bolts, pay attention to the force. It is better to use a torque wrench to prevent the flange from squeezing and deformation due to excessive force. Plastic diaphragm valve can be installed at any angle generally, but vertical installation is not recommended for large size plastic diaphragm valve especially size above DN125, because the large size diaphragm valve disc is made of cast iron, and vertical installation is easy to make the disc move downward due to the heavy weight of cast iron disc, the diaphragm will displacement over time and may cause leakage. UPVC diaphragm valve and CPVC diaphragm valve have socket bonding connection. When connect, release the union, glue one end, wait for the glue dry then glue the other end, tighten the union after glue dry of both side. PPH diaphragm valve and PVDF diaphragm valve has welding connection. One side shall be welded first, and the other side welded after.
Plastic diaphragm valves are generally weir type. The diaphragm is made of rubber or PTFE, which does not have good wear resistance. Therefore, hard particles should be avoided in the medium to avoid leakage caused by abrasion of the diaphragm. Plastic diaphragm valve use rubber seals between the valve body and the bonnet. After a period of use, the leakage may be happen due to the change of rubber elasticity. to re tightened the bolts will solve some leakage problems. The trim of the plastic diaphragm valve are isolated from the medium by diaphragm, so the trim is not easy to be damaged. However, if there is corrosive gas in the working environment, the corrosive gas may enter into the valve cover, cause the corrosion of the valve stem and the stem nut, and affecting the service performance of the valve. Therefore, if there is corrosive gas in the environment, the stainless steel valve stem is recommended. Although the diaphragm valve has the function of regulating the flow, it is not recommended to keep the valve in the half open position for a long time, which will cause serious wear to the diaphragm. During the service time, diaphragm wear is a common situation, but it is not recommended to replace the diaphragm, because the plastic material is sensitive to the temperature change, and the plastic diaphragm valve will inevitably have some deformation after long-term use, even if the diaphragm is replaced, it may still leaks, because the new diaphragm not fit the used body very well.