Globe Valves Types And Selection Principles
The stem axis of the globe valve is perpendicular to the seating seal surface, valve stem opening or closing stroke is relatively short, the valve disc once in the open condition, its valve seat and disc sealing surface between the no longer contact, and has a very reliable cutting action, making the cut-off valve products suitable as a medium for cutting or regulating and throttling use. Once the cut-off valve is in the open state, the valve seat and disc sealing surface between the no longer contact, so the cut-off valve sealing surface mechanical wear less. Since most of the valve seats and discs are easier to repair or replace the seals without having to remove the entire valve from the pipeline, this is a good fit for the welding of valves and pipelines. The flow direction of the medium through such valves has changed, so the flow resistance of the cut-off valve is higher than that of other valves.
The most obvious advantages of the cut-off valve are: in the opening and closing process, because the disc in the valve body sealing surface between the friction than the valve smaller, and thus wear-resistant. The cut-off valve opening height is generally only 1/4 the diameter of the seat passage, so it is much smaller than the gate valve. Usually there is only one sealing surface on the valve body and disc, so the manufacturing process is better and convenient for maintenance.
The selection principle of the cut-off valve is:
1. High-temperature, high-pressure medium pipe or device should choose the cut-off valve. such as thermal power plants, nuclear power plants, petrochemical systems, high temperature, high-pressure pipe on the road.
2. The cut-off valve is used in the pipe on the road where the convective resistance requirements are lax. Where there is little consideration of pressure loss.
3. Small valve can choose needle valve, instrument valve, sampling valve, pressure needle valve and so on.
4. There is flow regulation or pressure regulation, but the adjustment accuracy is not high, and the pipe diameter is relatively small, such as the nominal channel ≤50mm pipe, it is advisable to select the cut-off valve.
5. The small chemical fertilizer and the big chemical fertilizer in the synthesis industrial production should choose the nominal pressure PN160 nominal pressure 16MPa or PN320 nominal pressure 32MPa high pressure angle type cut-off valve or the high-pressure angle type throttle valve.
6. Alumina Bayer process in the production of silicon removal workshop, easy to coking of the pipeline, the choice of valve body separate type, seat can be removed, cemented carbide sealing pair of DC-type cut-off valve or DC-type throttle valve.
7. In the city construction water supply, the heating project, the nominal circulation small pipeline, may choose the cut-off valve, the balance valve or the plunger valve, if the nominal path is smaller than the 150mm Tube road.
The common cut-off valves have the following types:
1. Angle stop valve: In the angle stop valve, the fluid only needs to change One direction, so that the pressure drop of the valve is smaller than the normal structure of the cut-off valve.
2. DC-type cut-off valve: in the DC or Y-shaped cut-off valve, the flow of the valve and mainstream line into a slash, so that the destruction of the flow state than the conventional valve is smaller, thus through the valve pressure loss is correspondingly small.
3. Plunger-Type globe valve: This form of cut-off valve is the normal cut-off valve variant. In the valve, the disc and seat are usually designed based on the plunger principle. The disc polishing plunger is connected with the stem, and the seal is achieved by two elastic seals sheathed in a plunger. Two elastic seals are separated by a set of rings, and the seals around the plunger are pressed by the load exerted on the bonnet by the bonnet nut. Elastic seals can be replaced by a variety of materials, the valve is mainly used for "open" or "off", but with a special form of plunger or specific ring, can also be used to regulate the flow.