Characteristics and use of globe valve
Features and USES of globe valve:
A globe valve is a valve in which the closing member (disc) moves along the center line of the seat. According to this type of disc movement, the change of seat opening is directly proportional to disc travel. Because of this type of valve stem opening or closing stroke is relatively short, and has a very reliable cut-off function, and because of the change of valve seat opening and disc stroke is proportional, very suitable for the flow regulation. Therefore, this type of valve is very suitable for cutting or regulating and throttling.
Once the disc of pneumatic globe valve is moved from the closed position, there is no longer contact between its seat and the sealing surface of the disc, so its sealing surface has little mechanical wear, so its sealing performance is very good, the disadvantage is that the sealing surface may be clamped between the particles in the flowing medium. However, if the disc is made into a ball of steel or porcelain, this problem can be overcome. Because most globe valves have seats and discs that are easy to repair or replace, and do not require the entire valve to be removed from the line when repairing or replacing the sealing element, this is especially true where the valve and the line are welded together.
Due to a change in the flow direction of the medium through such valves, the Z small flow resistance of electric globe valves is also higher than that of most other types of valves. However, this condition can be improved depending on the body structure and stem layout relative to the inlet and outlet channels. At the same time. Due to the small travel between the globe disc opening and closing, and the sealing surface can withstand multiple opening and closing, it is suitable for frequent switching occasions.
The obvious advantages of globe valves are:
(l) in the process of opening and closing, the friction between the disc and the sealing surface of the valve body is less than that of the gate valve, so it is wear-resistant.
(2) the opening height is generally only l / 4 of seat channel diameter, so it is much smaller than gate valve.
(3) usually there is only one sealing surface on the valve body and disc, so the manufacturability is better and it is easy to maintain. However, the disadvantages of oxygen globe valve can not be ignored. The main disadvantage is that the coefficient of flow resistance is relatively large, resulting in pressure loss, especially in the hydraulic device, this pressure loss is particularly obvious.
The globe valve is mainly used for cutting off in the pipeline. Globe valves have the following advantages:
1. In the process of opening and closing the sealing surface friction is less than the gate valve, wear resistance.
2. Low opening height.
3. Usually there is only one sealing surface, with good manufacturing process and easy maintenance.
Globe valve is generally used, but due to the large opening and closing torque and long structure length, the nominal diameter is generally limited to DN≤200mm or less. The fluid resistance loss of the globe valve is large. This limits the wider use of globe valves.
There are many types of globe valves, which can be divided according to the position of the thread on the stem:
One, on the thread stem stop valve
Globe stem threads outside of body. Its advantage is that the valve stem is not eroded by the medium, easy lubrication, this structure is more common.
Two, down thread stem stop valve
Globe stem threads in body. The stem thread of this structure is in direct contact with the medium, susceptible to erosion and is not lubricated. This structure is used for small diameter and low temperature.
According to the valve channel direction, can be divided into; Straight through globe valve, Angle globe valve and three-way globe valve, the latter two are usually used to change the flow direction of the medium and distribute the medium.
Insulation globe valves can be used in most media flow systems. Various types of globe valves have been developed for various USES in petrochemical, electric power, metallurgy, urban construction and chemical engineering sectors.
The use of globe valve is very common, but due to the opening and closing torque is large, the structure length is long, usually nominal diameter is limited to 250mm below, also to 400mm, but the choice of the need to pay special attention to the import and export direction. Generally, the globe valve medium below 150mm mostly flows in from the lower part of the disc, while the globe valve medium above 200mm mostly flows in from the upper part of the disc. This is due to the consideration of valve closing torque. In order to reduce the opening or closing torque, generally more than 200mm of the globe valve are equipped with internal bypass or external bypass valve.