The way of medium flow for globe valves
A globe valve is designed to allow medium flow under the seat, with the aim of making the flow resistance small and saving effort when opening the valve. At the same time, when the valve is closed, the gasket between the valve casing, the valve cover and the packing around the valve stem are not subjected to force, and the long-term exposure to the medium pressure and temperature can prolong the service life and reduce the probability of leakage. In addition, the valve can be replaced or added with the valve closed for maintenance. Many people think that globe valves allow medium flow under the seat in every situation, but they are not. Under normal circumstances, globe valves allow medium flow under the seat, but there are some special cases where globe valves allow medium flow above the seat:
High pressure globe valves with diameter bigger than 100mm
Due to the poor sealing performance of the large diameter valve, in this way, the globe valve is in the closed state, and the medium pressure acts on the valve flap to increase the sealing of the valve.
Two globe valves connected in series on the bypass pipes
The second globe valve requires allowing medium flow above the seat.
Boiler exhaust and venting stop valves
Boiler exhaust and venting stop valves are only used during the boiler start-up process. The frequency of opening and closing is low, but the working fluid often loses due to poor sealing. For this reason, some power plants have to install such globe valves in order to improve the tightness.
Generally, it is difficult to close the valve with flow direction from under seat to up towards the disc under large diameter and high pressure. If the standard flow direction is used under high pressure and large diameter, the valve stem is easily deformed and bent by water pressure for a long time, which affects the safety and sealing of the valve; If the height is low, the diameter of the stem can be small, which will save costs for manufacturers and users.
High pressure globe valves with diameter bigger than 100mm
Due to the poor sealing performance of the large diameter valve, in this way, the globe valve is in the closed state, and the medium pressure acts on the valve flap to increase the sealing of the valve.
Two globe valves connected in series on the bypass pipes
The second globe valve requires allowing medium flow above the seat.
Boiler exhaust and venting stop valves
Boiler exhaust and venting stop valves are only used during the boiler start-up process. The frequency of opening and closing is low, but the working fluid often loses due to poor sealing. For this reason, some power plants have to install such globe valves in order to improve the tightness.
Generally, it is difficult to close the valve with flow direction from under seat to up towards the disc under large diameter and high pressure. If the standard flow direction is used under high pressure and large diameter, the valve stem is easily deformed and bent by water pressure for a long time, which affects the safety and sealing of the valve; If the height is low, the diameter of the stem can be small, which will save costs for manufacturers and users.