Outside Screw Stem Rising through Hand Wheel Type Gate Valves (Part One)

The outside screw stem rising through hand wheel type gate valve
An outside screw stem rising through hand wheel type gate valve adopts the structure that the nut of the valve stem is on the valve bonnet or the valve yoke. When the gate is opened and closed, the nut of the valve stem is made to rotate to rise the valve stem. Since this kind of structure is beneficial to the lubrication of the valve stem and makes the opening and closing process can be seen, the outside screw stem rising through hand wheel type gate valve has extensive applications.

The inside screw nonrising stem type gate Valve
An inside screw nonrising stem type gate valve adopts the structure that the nut of the valve stem is inside the valve body and it can have direct contact with media.

The gate is opened and closed by the rotatory valve stem. With the nonrising stem structure, the gate valve demands small installation space because the height of the gate valve remains unchanged. This advantage becomes more obvious when the gate valve has a large diameter or when the installation space is limited.

A gate valve with the nonrising stem requires an indicator for showing the extent of opening and closing of the valve itself. However, the inside screw nonrising stem type gate valve have the disadvantage of being easily damaged because the stem thread is unable to be lubricated and is directly corroded by media.

Major differences between the outside screw stem rising through hand wheel type gate valve and the inside screw nonrising stem type gate valve

First, the inside screw nonrising stem type gate valve has the lifting bolt rotating yet not moving up and down, and what can be seen is the valve stem only. The nut of the inside screw nonrising stem type gate valve is fixed on the gate and the gate is lifted by rotating the bolt. The outside screw stem rising through hand wheel type gate valve has lifting bolt of which the whole part can be seen. The valve nut of this kind of gate valve is not only close the hand wheel but also fixed, not rotating or moving up and down. Identical to the rising stem gate valve, the inside screw non-rising stem type gate valve has the rotatory bolt lifting the valve gate. But there is no relative axial displacement between the lifting bot and the gate. 

Second, the inside screw non-rising stem type gate valve has the lead screw which can not be seen from the outside of the valve. However, the lead screw of the outside screw stem rising through hand wheel type gate valve can be seen when the valve is operated. 

When opening and closing, the inside screw nonrising stem type gate valve has the hand wheel connected to the valve stem, which means there is no relative displacement between them. This kind of gate valve has the valve stem rotating around the fixed point to have the valve clack moving up and down.

Compared with the outside screw stem rising through hand wheel type gate valve, with the hand wheel staying at the fixed point, the outside screw stem rising through hand wheel type gate valve has the valve clack and the valve stem lifting up and down together.