Ensuring the valve’s tightness requires installing two series-connected shut-off valves. Due to the flow direction of the medium, the bypass stop valves are primary and secondary. In normal states, the primary and secondary valves are closed and in contact with the medium. The installation path of the valve needs high in and low out. High in and low out prevents the packing from being affected by the medium.
When opening, the globe valves are designed with an inlet low and outlet high to lower the flow and save effort. Conversely, the shut between the valve casing and bonnet is not stressed when the valve is closed. It will not be affected by the temperature and pressure of the medium for a long time. It also reduces the probability of leakage. Also, the stuffing can be added or changed when the valve is closed, which is easy for maintenance.
Globe valves are like forced sealing valves and block valves. Globe valves are also known as stop valves. The flow direction for globe valves is from top to base, so it has a directional installation flow. This type of globe valve is efficient for regulation and shut-off. And also, they have a very reliable cutting function. So, the valve seat opening change is directly proportional to the stroke of the valve disc. That’s why globe valves are very suitable for the regulation of flow.
Why does the globe valve with a diameter of less than 100MM have a low entry and high exit?
You should pay attention when inlet is high and outlet low of globe valves:
- High-pressure globe valves with a diameter greater than 100mm
- Due to the large-diameter valve, the fluid pressure increases the sealing of the valve.
- Two globe valves are linked in series on the pipeline. The second globe valve needs an “outlet low and inlet high.”
- For the bypass system.
- Back pressure and Balance the front of the main pipeline valve.
- Open and reduce the wear of the main pipeline valve.
- During staring, warm up the pipe with a small flow.
- The pressure above the speed of the boiler controls the water flow.
Why The Globe Valve Is Designed With Low Inlet And High Outlet Openings?
This section will find the main benefits of low inlet and high outlet. The use is to save effort and lower the flow resistance when opening the valve. The gasket between the valve housing and the bonnet is not stressed when the valve is closed. And the medium pressure has a slight tension on the valve stem and will not affect the valve stem.
The valve stem is also dipped in the medium and is not easy to corrode by the medium. This way, the valve stem protects, and the packing structure is isolated from the medium. It will ensure the medium on the packing and improve the life of the valve stem packing.
While working with inlets and outlets, the most important thing is safety. If the valve stem breaks, the valve can auto-open to avoid system overpressure.
Using a low inlet and high outlet can also widely avoid the water moistness process of the shut-off valve. When the valve is closed, the moving speed under the lubricating flap is slow. As a result, the closing time relatively becomes long, and it takes work to cause a water hammer process.
Why Do Globe Valves With A Diameter Greater Than 100mm Have High Entry And Low Exit?
Globe valves are most suitable for low leakage shut-off and regulation. As the valve size and pressure increase, the load on the stem becomes more significant. The pack also makes the valve challenging to work manually. This issue was first seen with steam engines when steam pressures rose to produce power.
The upper disc has inlet pressure on the top, while the lower disc has inlet pressure on the base. The spaces are unequal because of the differences in inner and outer seat diameters. This slight difference makes a small thrust for large high-pressure valves. Working by handwheel with rising stem valves can be considered for applications with other valves. They are also suitable for use on sites without power or emergency backup systems.
The valve has two pressure casings. The outer casing starts at inlet pressure, and the inner is at outlet pressure. The future flow moves around the case and through both seats into the inner container. Sealing in both directions is equal, so the flow in each direction exists.
Preparation before installing the globe valve
You should ensure that the shut-off valve logo is consistent with the use of the needs. And check that the media flow must be compatible with the direction pointed on the valve body by an arrow.
Before installation, check the sealing surface and globe valve channel. If there is dirt on the valve body, there should be a clean, soft cloth to wipe it away.
You should notice whether the manual device operation is flexible. When installing the shut-off valve, there is no jamming process. The shut-off valve operating process from the operating floor should be about 1.2m. When the hand wheel from the functional ground is more than 1.8m, it should be set to activate the function of the shut-off valve.
Globe valves are unidirectional and flow in one direction under the disc. The valve should be placed vertically where the handwheel operation will be at the top of the valve. The proper placement of the valve ensures that no premature damage or wear will occur to the valve.
Install the Globe Valve on The Pipeline
When installing a globe valve on a pipeline, ensure that the axis of the globe valve is parallel to the channel. Here are two methods to mount a valve on a pipeline. In the first step, you may use a plumb bob. A plumb bob is a weighted string with an eye at one end. The levels hang downward when you lower them over the centerline of your pipe.
- The second method is to use a laser level or other tool. Mark each valve’s position on the pipe so that when it’s time, install them all again.
- Install the gasket on the flange of the valve with nuts and bolts. Then pull all bolts open ends and then use a wrench to tighten them. To control leakage, choose a rubber gasket according to the pressure, temperature, and medium,
- The globe valve is installed between two pipes using a wrench to pull nuts on each side of the handle. The bolts are tightened clockwise until they can not turn them.
- If there is no leak, tighten the bolts more than half a turn and move it back off again. If you notice any leaks, pull or draw the bolts until the leak stops. But, if your installation is difficult to solve, it is best to contact an expert for help.
- Shortly you will pay attention to the main installation points below:
- Remove any debris from the valve
- Ensure the inside of the valve is free from moisture or water
- Ensure the valve is supported
- Ensure you have room to work the valve
- Do a complete dry cycle of the valve from closed to open, then back again.
- Tighten flange bolts slowly in a diagonal pattern
- Raise the internal pressure to allow the bolts to be installed correctly and the valve to be sealed
- Raise internal pressure to operate levels and check again
Summary
Generally, it is more comfortable to close the valve if the inlet low and outlet high are used under large diameter and high pressure. If inlet low and outlet high are used under high pressure and large diameter. As a result, the valve stem can easily deform under water pressure for a long time. The valve stem diameter can be smaller if the inlet high and outlet low are specified. It will also save some costs for valve suppliers and users.
The discs need a degree of flexibility to allow both seats to work correctly. The body is relatively complicated, and casting is the best construction technique. Connections can be in-line. Typical applications include isolating valves for steam and water turbine.
