Gate valves are very common in pipeline applications, so the chance of problems will naturally be high, today ZECO Valve introduces you to the various problems that may arise in industrial and water treatment under two types of working conditions and solutions.
Industrial Gate Valve Problems
Why do gate valves fail?
The most common causes of gate valve failure are wear and corrosion of the wedge and seat. The inner parts of a gate valve tend to wear over time. And corrosion can cause the wedge to stick in the open or closed position. When the handwheel is stressed, the stem leading from the handwheel to the wedge tends to break off, rendering the valve useless.
In addition, the stem packing and the bonnet gasket in the gate valve are wearing parts and need to be replaced within the period recommended by the manufacturer, which may also cause leakage if not replaced.
GATE VALVE REPAIR
Can I repair gate valves?
Yes, Please refer to the following problems and solutions
1.Problem: Leakage between gate valve and valve connection
First, check whether the bolts connecting the valve to the gate valve are tight, if not, its seal ring and flange sealing groove surface often lead to leakage if they are not sufficiently connected. Check that the bolts and nuts are in order and tighten all bolts until the seal is pressed. Next, check the size and accuracy of the seal and flange sealing groove surface, if the seal contact surface is the wrong size or too rough, repair or renew it. Also check the contact surface of the seal ring and flange sealing groove for defects such as a little erosion, sand holes, sand holes or impurities, if so, weld, repair or clean accordingly.
2.Problem: Leakage from bonnet
This failure phenomenon often occurs in the packing seal leakage.
Firstly, check that the seal fits correctly and is compatible with the seal groove, if there is a problem, the seal should be replaced or the seal groove repaired. Secondly, check if the seal has burrs, breaks, and twists off, if so, the seal should be replaced. Then, check the surface of the seal groove for roughness or other defects and if there are defects, remove them or renew the damaged parts.
When the bonnet or bracket uses compression seal packing, the installation of the packing should be checked and if the packing is found to be installed backward, it should be removed and installed according to the correct method.
3.Problem: Leakage from valve body cavity
During the casting process, sometimes casting defects may appear in the valve body, such as grit holes and sand holes. They are difficult to detect during machining without the requirement for non-destructive testing, but once pressure is applied to the valve body, hidden casting defects are exposed.
If this is the case, it can be welded, repaired, or renewed as appropriate according to the standard.
4.Problem: Leakage from valve seat and valve wedge
4.1 Leakage occurs on the valve seat and the valve wedge, which is the most common phenomenon during the installation or maintenance of gate valves. There are generally two types: one is leakage on the sealing surface; the other is leakage at the sealing root.
4.1-1.Corrective Action: The first thing to check is the accuracy of the sealing contact surface of the valve seat and the valve wedge. The sealing surface needs to be ground, and if there is a rough surface, remove and regrind it. Next, check the sealing surface for defects such as pockmarks, indentations, grit holes, cracks, etc. If this is the case, the seat and wedge should be replaced. For valve seats with compression springs, check that the spring force of the pressure spring meets the requirements, if the spring force is low, the compression spring should be renewed. In addition, check that the T-shaped coupling between the valve wedge and the stem is not too loose and that there is no slope, if so, the wedge should be removed and adjusted to the optimum size.
4.2 When installing the valve, it is easy to drop in foreign objects such as welding checks, scrap iron, and impurities.
4.2-1.Corrective Action: Clean up the debris before installation. If you forget to clean or clean incompletely, the valve wedge will not reach the desired closing depth and cause leakage, in which case the valve body should be removed and cleaned.
The valve seat should be installed using a special tool. Check that the valve seat is installed correctly, if the threads are less deep than expected the seat will leak, in this case, the seat should be installed using a special tool.
How do you fix a gate valve that won’t open or close?
The first possibility is that the valve torque is too large and requires more force to close or open, replace the actuator with a larger size
The second possibility is that, when the valve is installed in the pipeline, there is a build-up of welding slag or debris at the bottom of the valve blocking the gate to close, and the debris needs to be cleared. The third possibility is that the gate and the valve seat have been damaged and need to be repaired and replaced in time.
Refer specifically to section 4.
How to replace a gate valve, Replace gate valve with ball valve
Close the shut-off valve in front so that the medium is in a static state, and discharge the medium in this section of the pipeline, if it is a flange-connected gate valve, you need to remove the bolt and nut of the connection, clean the sealing surface, replace the gasket and reconnect the new ball valve. If it is a threaded connection gate valve, just screw it down. In the case of SW or BW connections, cut down and weld the new ball valve in place.
Water Gate Valve Problems
My gate valve is stuck and open, what should I do
If your gate valve is open and you cannot close it, then the only option is to drain it. In some cases, plumbers can quickly replace valves, but this does not pose a risk. In most cases, when your gate valve has a problem, if your gate valve is open, it is best to drain the water.
The problem that the gate valve cannot be opened
If you have a gate valve that cannot be opened, it is usually due to a broken spindle. The reason for this usually rest is that when the valve is closed due to not dirty build, scale, or other, the plumber or master will tighten the thread causing the thread to break. If the valve cannot be easily closed, it is best to replace the gate valve while draining water, to further avoid gate valve problems and cause more costs.
How to replace the gate valve without losing hot water
The best way to replace the valve is to freeze the pipe first, and then replace the valve. The only other way is to close the gate valve and disconnect the bottom pipe. Once you leave the top nut of the supply pipe, you can switch the valve very quickly. This must be done by a skilled emergency plumber.
My gate valve can’t close properly, why?
The reason why the valve cannot be closed normally is that as the gate valve ages, you will find dirt or scale accumulation, causing the closing mechanism to fail to close normally. The best way to solve this problem is to either clean the valve thoroughly or replace the gate valve.
When replacing the gate valve, whether it must be emptied first
As explained in the previous paragraph, to replace any valve, you don’t always have to empty it, as long as you have the experience and tools to do so.
What causes the gate valve to rupture
The reason for the rupture of the gate valve is that the valve is fragile and the pressure is too high when the gate valve is closed. The spindle thread is not deep enough to enter the valve, so if the pressure is too great, there is not much room to stop any resistance. It’s a bit like breaking a twig instead of breaking a stick.
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