Ascending Efficiency: Rising Stem Valves in Critical Process Control
Nov 21,2023Read More
The length of gate valves is shorter than globe valves, but the height is higher than globe valves. We should pay attention to the height when installing the stem gate valves, if the installed space is limited, choosing the suitable valves is very important. Gate valves can be closed with sealing face tightly according to the medium’s pressure, so that will not have risk of leakage. In opening and closing, the trim always contact & rub with seat ring’s sealing face, the sealing face will easily be abraded. When gate valves is nearly to be closed, the pressure between pipeline’s front and behind is larger, so the sealing face will be abraded more seriously.
The difference between gate valves and globe valves in principle is: a globe valve is rising stem type so the hand wheel is rotating and rising with stem together; gate valve is rotating hand wheel, rising stem and non rising stem. The flow is different from each other, gate valves are fully opened or fully closed, but globe valves not need that. Globe valves have the direction requirement for flow’s import and export, but gate valves have no need.
Explain: Gate valves' pipeline is just like the straight pipe, but there is a gate in the pipe content, if the gate lift up the door will be fully opened. The fluid in globe valves will turn 180 degrees, always into the valves from one side then turn 90 degrees and flow upper, once flowing to the top side then turn 90 degrees and flow out. So there is a bonnet setting on the exit place where fluid flowed upper, once the bonnet closed the globe valve closed, once the bonnet opened the globe valves opened.
For globe valves, fluid is into from the lower side and out from the higher side, the pipeline is not on the same level from the appearance. The gate valves' flow pipe is on the same level.
Explain: From the side of flow resistance, if fully opened, the gate valves’ flow resistance is smaller than globe valves. The normal gate valves’ flow resistance is nearly 0.08~0.12, can be easily opened and closed, the medium can flow from two sides. The normal globe valves’ flow resistance is 3-5 times of gate valves, need be closed mandatory then get sealing. The globe valves’ trim contact the sealing face only on the time of fully closed, so the sealing face just abrades a little.
1) Base on the gate valves’ flow direction, the effects are the same no matter the fluid goes into from which side.
2) There are two installed ways for globe valves. One is that medium goes into the valve from the below of trim. The advantage is that when the valve is closed, the coil will not have pressure so the service life of the coil can be prolonged, and can replace in the case of the pipeline under the pressure. The disadvantage is that the valves’ driving torque is larger, about 1 time of the flow from the upper, the stem is easy to be bent under large axial force. So such a way is just suitable for globe valves which size range smaller than DN50, the globe valves which size range larger than DN200 always choose the way that medium goes into from the upper. (The electrical globe valves usually take the way that medium go into from the upper.) The disadvantage of medium entering from the upper is opposite with the medium entering from the below.
Globe valves’ sealing face is a small trapezoidal side of the trim (see the shape of the trim), once the trim dropped off, just as the valve is closed (if the pressure difference is large, of course, the valve will not close strictly, but the check effect is good). The gate valve is sealed by the side of the trim gate, the sealing effect is worse than globe valves, if the trim is dropped off will not like the globe valve just as the valve is closed.
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