1. The valve rod of straight stroke pneumatic control valve is thin
It involves a simple mechanical design basis: large rolling friction, small rolling friction. The stem of the straight travel valve keeps fit from left to right. If the packing is slightly tightened, it will wrap the stem too tightly, causing a large backlash. Therefore, the valve rod design scheme is very subtle, and tetrafluoro packing with small friction resistance is common in the packing, which is convenient to reduce the return difference. However, the difficulty of dispatching is that the valve rod is thin, which is easy to bend, and the service life of the packing is also short. The effective way to deal with this problem is to use the travel valve stem, that is, the angle travel regulating valve stem. Its stem is 2 to 3 times thicker than the straight travel valve stem. In addition, it uses high-purity graphite packing with a long life. The bending stiffness of the stem is good, the packing has a long life, and its friction torque is small and the backlash is small.

Equipment type compensator
1 Corrugated compensator
This is a compensator made of corrugated stainless steel sheet. Each compensation has 3-6 wave nodes. Due to weak ripple strength, small compensation ability and large axial thrust, it is applicable to pipes with pipe diameter>150 mm and pressure<0.6 MPa. The corrugated compensator manufactured today was once suitable for 1.6 MPa pressure.
2 Packing type compensator (also called sleeve type compensator) This is a compensator made by applying inner and outer tube inserts to stop expansion. The inner pipe is called the core pipe, and the outer pipe is called the sleeve. There is a packing joint chamber between the two pipes. There are one-way and two-way packing compensators. The compensation ability of one two-way compensator is equivalent to that of two one-way compensators. The compensator is used for the working pressure of 1.6 MPa, and is used on the thermal pipeline where it is difficult to use the square compensator. Due to the insecure sealing of the packing, it is necessary to monitor at any time during the operation, and supplement or replace the packing in time. It is not suitable for use in inaccessible trenches and small inspection rooms.
3 Spherical compensator (also called angular compensator) This kind of compensator applies the random bending of spherical pipe to deal with the compensation problem of the pipeline, and is most suitable for the three-way displacement parts of steam and hot water pipelines. The compensator can be installed at any position, and the working medium can enter and exit from either end. The defect is lateral displacement and leakage. Before installation, both ends must be blocked, stored in a dry and ventilated room, and checked regularly to avoid corrosion.
4 Selection of guide line
According to the analysis of the safety, working life and technical economy of the compensator, the selection order of the compensator is: natural compensator, square compensator, corrugated compensator, packing compensator and spherical compensator. Since the natural compensator and square compensator use a local pipeline as compensation, there is no additional equipment, but only some additional pipelines. The service life of these two compensators is basically the same as that of the pipeline, while the other three compensators cannot reach the service life of the pipeline, and sometimes they are far from each other. Due to the fixed pipe position of all professional pipelines in the urban road planning, the square compensator cannot be used; Long interval roads have no break points, and natural compensators cannot be used. Therefore, these two compensation methods are mainly used for yard pipe network. Ball type compensators can only be used on special pipe sections, so today's applications are mainly corrugated and packed compensators.