Outside Screw Stem Rising through Handwheel Type Gate Valves (Part Two)

According to the position of the screw of the valve stem, the gate valve is divided into the outside screw stem rising through handwheel type gate valve and the inside screw non-rising stem type gate valve.

An outside screw stem rising through hand wheel type gate valve adopts a gate as its disc. The gate has the direction of the motion perpendicular to the flow direction of fluid. This kind of gate valve can not regulate and throttle the flow because the valve can only be opened and closed completely.
 
A gate of the gate valve with rising stem has  two sealing surfaces, and the sealing surfaces of the most commonly used gate valves' gates form in the shape of a wedge. To improve the manufacturing technology of the gate valve and avoid angular misalignment of the sealing surface formed in the process of manufacturing, the gate of the wedge-shaped gate valve can be made the flexible gate with a little deformation. Moreover, the valve gate can also be made the solid gate integrated with the valve body.

When outside screw stem rising through handwheel type gate valves is closed, the sealing surface is sealed by the pressure of the media only, that is, the sealing surface of the gate being pressed by the medium pressure to the other side of the valve seat on the valve body. This kind of sealing structure is called self-sealing structure.

The working principle of the outside screw rising through handwheel type gate valve
To open or close the outside screw rising through hand wheel type gate valve, the hand wheel will be rotated and then the gate connected to the valve stem will be lifted up or brought down. 

Advantages of outside screw stem rising through handwheel type gate valves
Small flow resistance, little erosion or corrosion of the media to the sealing surface

Able to save efforts in opening and closing the valveUnlimited direction of the media, no disturbed flow, no need to reduce the valve's pressure

Simple structures, extensive applications, good manufacturing technologies

Disadvantages of outside screw stem rising through handwheel type gate valves
More erosion and corrosion between two sealing surfaces, difficult maintenance

The large volume requiring a certain operating space and a long time to start open and close the outside screw stem rising through hand wheel type gate valve

Installation and maintenance of outside screw stem rising through handwheel type gate valves
The handwheel, the handle and the transmission mechanism of the outside screw stem rising through handwheel type gate valve are not allowed to be hit and be used for hoisting anything. 

With double discs, the outside screw stem rising through handwheel type gate valve must be installed in the vertical position, that is, the valve stem being installed in the vertical position and the handwheel being installed on the top of the valve body.

In order to balance the differential pressure between the by-pass valve and the gate valve, and reducing opening force, the by-pass valve combined with the gate valve should be opened first.

With the transmission mechanism, the gate valve has to be installed according to the installation manual.

The gate valve with rising stem need to be lubricated once a month if it is used frequently.