globe valve, also known as the cut-off valve, belongs to the mandatory sealing valve, is a kind of truncated valve. there are three types of connection: flange connection, screw connection and welding connection.
our country valve "3 turn to give" ever made provision, the flow direction of stop valve, uniform use from top to bottom, so installation from time to time directionality.
this type of stop valve is ideal for cutting off or regulating as well as throttling. due to this kind of valve stem open or close stroke is relatively short, and has a very reliable cutting off function, and because of the change of valve seat opening and disc stroke proportional to the relationship, it is very suitable for the regulation of flow.
globe valves are designed to be low in feed and high in height to provide low flow resistance and ease of opening the valve. at the same time when the valve is closed, the gasket material between the valve shell and the valve cover and the packing material around the valve stem do not bear the force, will not be affected by the medium pressure and temperature for a long time can extend the service life, reduce the probability of leakage. in addition, the valve can be closed in the state of replacement or add filler, easy to maintain.
many people think that the globe valve is low into high, in fact, it is not. in general, globe valves are low in and high out. however, in some special cases, globe valves are high in and low out:
1. high-pressure globe valve with a diameter of over 100mm
due to the poor sealing performance of large diameter valve, the use of this method of cut-off valve in the closed state, medium pressure action on the top of the disc, in order to increase the sealing of the valve.
2. two globe valves in series on the bypass pipeline. the second globe valve requires "high inlet and low outlet".
in order to ensure the tightness of the valve in a maintenance cycle, the valve which is often opened and closed should be equipped with two series stop valves. for the bypass system, the installation of the bypass has the following functions:
(1) balance the pressure before and after the main pipeline valve, make it easy to open the province, reduce the main pipeline valve wear;
(2) start the process of small and medium flow warm pipe;
(3) on the main feed water pipeline, control the feed water flow to control the boiler booster speed of the boiler water pressure test. according to the direction of medium flow, the bypass globe valve is a primary valve and a secondary valve, and the primary valve and the secondary valve are closed during normal operation of the unit, both of which are in direct contact with the medium. in order to prevent the secondary valve shell and cover between the gasket and stem around the packing for a long time by the medium and temperature action, and in the process of operation can replace the valve packing, the secondary valve requires the installation direction "high in low out".
3. vent the stop valve
the blow-off globe valve is only used in the process of boiler starting water supply, with a small opening and closing frequency, but it often causes the loss of working medium due to the lax sealing. for this reason, some enterprises install this kind of globe valve in the direction of "high in and low out" in order to improve the tightness.
4. electromagnetic quick break valve
the function of the solenoid quick break valve is to close quickly and quickly cut off the fuel supply. the structure of the solenoid quick break valve and the structure of the globe valve is similar, if the solenoid quick break valve is also working medium from the lower into, the upper outflow, then the fuel role in the lower part of the solenoid quick break valve disc force is very large, and the heavy hammer of the solenoid quick break valve is far less than it. therefore, if the working medium enters the quick break valve from the lower part, the torque generated by the heavy hammer is less than the torque generated by the fuel pressure, and the fuel cannot be cut off when the quick break valve operates, thus the expected purpose cannot be achieved. if the working medium enters from the upper part of the quick break valve, the pressure behind the valve will decrease rapidly once the quick break valve is operated, and the force of fuel acting on the lower part of the valve disc will soon drop to zero.
in general, it is difficult to close the valve if low inlet and high pressure are used under large diameter and high pressure. if low inlet and high pressure are used under large diameter, the valve stem will be easily deformed and bent by water pressure for a long time, which will affect the safety and tightness of the valve. the valve stem diameter can be smaller if the high inlet and low inlet are selected, which will also save some cost for manufacturers and users.