Flow of the regulating valve is identified direction arrow on the valve body, usually install regulator, to make the direction arrow on the body are consistent with the flow direction of modulated medium,
But due to differences in production site, to the use requirements of the regulating valve is also each are not identical, practice shows that the flow of control valve will affect the valve working characteristic, and directly affect the normal operation of the control system or not,
Regulating valve according to the flow direction of medium is divided into different type "flow" and "flow closed type two kinds, flow is not at the same time, the stress of the regulating valve valve core are also different, such as valve before the pressure effect on the valve core, has a tendency to open the valve core, become the" flow "type; On the other hand, have the pressure to the valve seat valve core, close the valve of trend, become "flow closed type", from the flow direction of medium on the valve core to open, "flow" type medium flows from the small head toward the big end of valve core, the big end "flow closed type" media from the valve core to small head flow, flow control valve to affect the performance of use,

Small diameter and high pressure valves, if the flow to flow type closed type, its service life can be greatly extended, this is because the flow towards open open type medium flow, cavitation, erosion main effect on the seal, and make the root valve core and valve seat sealing surface damage soon; Towards closed closed type medium flow and flow, cavitation, erosion effect after the throttle valve seat sealing surface, under the protection of the sealing surface and the valve core is the root, so as to prolong the service life of the regulating valve,
Sometimes because of increased production, or calculation, choose mistake make regulating valve flow coefficient partial hours, valve fully open also can't satisfy the production, change the flow methods are available, and the change of flow used for flow closed type to open type, it can make the control valve by 10% ~ 15% more traffic,
Flow and flow type closed type two kinds of flows to each have advantages and disadvantages, so it is necessary to the flow of correct selection of regulating valve is, when the choice should choose according to actual working condition, such as many devices require regulator can be shut off completely working medium, the closing of the valve is a main requirement, should choose "flow closed type", if the selected is single-seat valve, the valve is to coincide with the valve body by the arrow on the contrary, Angle and pressure valve, cavitation is serious, life is short, also should choose "flow closed form", and can improve the service life of the valve, the valve stem seal occasions with strict requirements, to prevent leakage, should choose to "flow" type, for suspending liquid, high viscosity, medium containing solid particles, to prevent leaks, jams, should choose "flow closed type",
The same kind of the flow are not necessarily the same valve type, such as small diameter of the high pressure valve, its working pressure difference is higher, cavitation is serious, life is short, should choose "flow closed type", but for large diameter high pressure valve, its working pressure but the pressure difference is not too big, still should choose to "flow" type is completed, because the "flow" type stability is good, can not use the measures to prevent the oscillation,
Due to "flow" closed the flow capacity of 10% ~ 15% larger than the "flow" type, when the direction of "flow" type install valve fully open flow also can not meet the technical requirements, can be changed to "flow closed type" solve temporary difficulties,
With "flow closed form poor stability", choose "flow closed form", after stability become major problems, due to valve work again small open degree easy oscillation, so should try to minimize the valve opening in 30% ~ 40%, want to choose the actuator spring stiffness big, should be matched with the valve positioner used when necessary, the valve to change, change will make the flow capacity and flow characteristic, it is bound to have impact on the control system, so the change valve flow direction, the above problems should also be considered appropriate,