Valves which are devices used to control the flow of fluids, have found their way into industrial applications worldwide. There are many things to consider, when it comes to purchasing manual valves. In order to pick the appropriate one for your system, knowing its different types and applications is a must. Linquip has compiled useful information on these types of valves. So follow this new blog to find out more about them.
What are manual valves?
Manual valves are those valves that operate through a manual operator such as a hand-wheel or hand-lever, which are primarily used to stop and start flow, although some designs can be used for basic throttling.
The best manual valves for on off service are those that allow flow to move straight through the body, with a full-area closure element that presents little or no pressure drop. Usually if a manual valve is used to start and stop flow, as an on off valve, and the manual operator is placed in a mid-stroke position, partial flow is possible as a throttling valve. However, some on off designs in a mid-stroke position are not conducive to smooth flow conditions and may even cause turbulence and cavitation.
Different Types of Manual Valves
Manual valves can be categorized into 6 main types, based on their operating mechanism.
- Ball Valves: Ball valves offer very good shut-off capabilities. A simple quarter-turn (90°) completely opens or closes the valve. This characteristic minimizes valve operation time and decreases the leakage chances due to wear from the gland seal.
Manual ball valve can be divided into two categories: reduced bore and full bore. In reduced bore valves, the valve opening is smaller than the diameter of the piping; in full bore valves, the valve opening is the same size as the diameter of the piping. Full bore ball valves are often valued because they minimize the pressure drop across the valve.
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- Butterfly Valves: In butterfly valves, the flow is regulated through a disc-type element held in place in the center of the valve by a rod. Similar to ball valves, valve operation time is short because the valving element is simply rotated a quarter turn (90°) to open or close the passageway.
Butterfly valves are characterized by their simple construction, lightness in weight, and compact design. Their face-to-face dimension is often extremely small, making the pressure drop across a butterfly valve much smaller than globe valves. Materials used for the valving element and sealing can limit their applications at higher temperatures or with certain types of fluids. Butterfly valves are often used on applications for water and air, and in applications with large pipe diameters.
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- Globe Valves: The globe valve is suitable for use on a wide variety of applications, from flow rate control to open/close operation.
In this type of valve, flow rate control is determined not by the size of the opening in the valve seat, but rather by the lift of the valve plug. One feature of these valves is that even if used in the partially open position, there is less risk of damage to the valve seat or valve plug by the fluid than with other types of manual valves. Among the various configurations available, needle type globe valves are particularly well suited for flow rate control.
Another point to consider about globe manual valves is that the pressure drop across the valve is greater than that of many other types of valves because the passageway is S-shaped. Valve operation time is also longer because the valve stem must be turned several times in order to open and close the valve, and this may eventually cause leakage of the gland seal (packing). Furthermore, care must be taken not to turn the valve shaft too far because there is a possibility it could damage the seating surface.
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- Gate Valves: The construction of a gate valve is similar to that of a floodgate: flow is controlled by raising or lowering the valving element, which is generally available in three different types: solid (plain), flexible, and split. The latter two types help prevent the valving element and body from being deformed due to various operating conditions.
Like ball valve, this type of manual valves is not usually used to regulate flow. One of the reasons for this is because the valving element can be damaged when in the partially open position. Similarly, they also limit the pressure drop across the valve when fully open. However, setting the valve to the fully open or closed position requires the handle to be turned many times, which generally makes these valves have the longest operating times among those valve types mentioned here.
- Check Valves: There are various types of check valves and location of these valves should be selected carefully. For pumps, the check valve should be placed four or five diameters of the pipe away from the pump, otherwise turbulence from the pump can cause the valve disc to flutter and wear the bearings. Vertical lines are poor location for check valves.
This type of manual valve is mainly used for preventing back flow. It is also used to prevent air inflow into pipeline filled with water and to minimize water hammering.
- Plug Valves: they are either lubricated or non-lubricated type. 90 degree turn of the valve fully opens or closes this valve and therefore plug valve is known as quarter turn type of valve. The design of the plug valve is such that solids do not accumulate and cause a jam. The valve can be fixed in an open or closed position for a long period of time.
Both types are rarely used for isolation. Lubricated type is used if the valve in a system needs to be closed for extended time period or if it is high pressure system and can be used were tight seal is required especially in high pressure (above 150 psi) systems.
- Diaphragm Valves
Diaphragm valves use a pinching method to stop the valve flow using a flexible diaphragm. They are available in two types: weir and straight-way. The most commonly seen of the two is the weir-type. This is because the straight-way type requires additional stretching of the diaphragm, which can shorten the diaphragm’s life-span.
One of the major advantages of using these types of manual valves is that the valve components can be isolated from the process fluid. Similarly, this construction helps prevent leakage of the fluid without the use of a gland seal as seen in other types of valves. One the other hand, the diaphragm becomes worn more easily and regular maintenance is necessary if the valve is used on a regular basis. These types of valves are generally not suited for very high temperature fluids and are mainly used on liquid systems.
So this is everything you need to know about manual valves and their applications within a system. Want to share your experience with different valves in Linquip? We will be more than glad to read your viewpoint in the comment section. If you have any question regarding the topic, feel free to sign up on our website and get the most professional advice from our experts.
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