Upward and downward Stem of Gate valve

Gate valve is a linear motion valve used to start and stop the flow of fluid. It’s a full opening/closing valve. Disc or gate used to start or stop the flow which is operated through a combination of stem and handle. Upward and downward linear motion of stem causes the opening and closing of the gate valve.

When the valve is the fully open condition, disc or gate fully removed from the flow path and provide no resistance for flow. This no resistance causes a minimum pressure drop. When the valve fully closed, disc to seal ring contact surface for 360 degrees and provides a tight seal. Therefore, very little or no leakage through disc when the valve at full closed.

On the opening of the gate valve, a large amount of working fluid flow in nonlinear manners (directionless flow) with respect to the gate opening percentage. Partial opening of the gate causes vibration in disc or gate due to fluid flow. Most of the flow change occurs near shutoff with a comparatively high fluid velocity causing disc and seat wear and eventual leakage if used to regulate flow. For all these reasons, the gate valve not used for throttling of flow.

Rising Stem Gate Valve:

In a rising stem gate valve, stem raised from the flow path when the valve is open.  During the opening of the rising stem gate valve, stem along with gate moves upward while closing, stem along with gate moves downward. In simple words, the stem is not vertically stationary in stem rising gate valve. Rising stem clearly see when the valve is open. It means the rising stem is the physical indication of valve opening. Rising stem valves are available in two basic designs. Some valves have a stem that rises through the hand wheel and some have a stem that is the thread to the bonnet.

Non-Rising Stem Gate Valve:

                                         

In a Non-rising stem gate valve, no upward or downward movement of stem outside the valve body. The stem internally threaded and remains vertically stationary. When the hand wheel on the stem rotates, gate or disc moves upward or downward on the internal threads but stem remains vertically stationary.

Non-Rising Gate Valve

In simple words, in non-rising stem gate valve, gate moves vertically up and down while stem remains stationary. These valves provided with pointer-type indicator threaded onto the upper end of the stem to indicate valve position. These valves are used where less space is available for valve operation and the medium is less corrosive for stem material.

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