Valve Selection And Examples

The valve is a control component in the fluid delivery system, has many functions such as cut-off, regulation, diversion, prevent backflow, regulator, shunt or overflow relief.

Valves are widely used for fluid control systems, ranging from the simplest sanitary shut-off valves to a variety of valves, used in extremely complex control systems, with a wide variety of specifications. Sanitary valves can be used to control the flow fluids such as air, water, steam, corrosive media, mud, oil, liquid metal and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves, chrome molybdenum steel valves, chrome molybdenum vanadium steel valves, duplex steel valves, plastic valves, non-standard custom valves.
Butterfly Valves
Valve selection steps:
1. According to the pressure of the valve, caliber, the media has been the temperature and the temperature can be selected to adapt to the valve model.
2. Know the way the pipe connection and the caliber of the valve can determine the way the valve is connected.
3. The use of the valve If you know and the conditions of the production process, then you can determine the valve drive device.
4. The general diameter of the valve is the diameter of the pipe, but also according to the pipe diameter to calculate the real use of the valve caliber.
5. To determine the sealing surface of the valve to know what the valve is the medium, temperature and pressure values, the maximum use of the valve body temperature must be greater than the medium temperature.
6. Valve nominal pressure to determine the body according to the material, the media working pressure and temperature.
7. Valve characteristics of the media, working pressure and temperature, you can choose the model and sealing surface.
valve fittings
Valve selection example:
Steam pipe working pressure is 13 kg, the temperature is 350 degrees Celsius, caliber is 100, to choose what kind of valve. From the above known conditions, first determine the material of the valve body, because the steam pressure is 13 kg, the temperature is 350 degrees Celsius, you can choose ductile iron or cast steel. However, from the temperature of 350 degrees Celsius to consider, then the ductile iron is more difficult to choose, so for safety reasons, should use cast steel valves. And then from the pressure to analyze, according to cast steel and long-term pressure temperature, the valve should choose 16 kg or 25 kg is appropriate. Next is the choice of sealing surface, to use stainless steel. And given the valve diameter is 100, diameter is relatively small, so the opening and closing time and torque are not large, then select the manual on it. Generally take the steam pipes are made of seamless steel pipe, and seamless steel pipe are used welding, but in order to make the valve easy to install and repair, it is recommended to use the flange connection.

Read More

Six Solutions to The Leakage of Control Valves

Six solutions to the leakage of the control valve
1) Increasing the sealing grease method
For valves that do not use sealed grease, can increase the sealing grease to improve stem seal performance.

2) Increasing the packing method
In order to improve the sealing performance of the packing on the stem, a method of increasing the packing may be used. Usually using double-layer, multi-layer mixed filler form, simply increase the number, such as 3 to 5, the effect is not obvious.

valve fittings

3) Replace the graphite packing method
Large use of PTFE filler, because of its operating temperature is in the range of -20 ~ +200, when the temperature is in the upper and lower limits, changes in the larger, the seal will be significantly reduced, aging fast, short life. Flexible graphite fillers can overcome these shortcomings and long service life. So some of the factory all the PTFE filler to graphite filler, and even the newly purchased control valve will be one of the PTFE filler into graphite filler after use. But the use of graphite filler hysteresis, and some also have a crawling phenomenon, which must be considered.

Divert Valves

4) Changing the flow direction, set P2 in the stem end method
When the △ P is large, P1 is large, the seal P1 is clearly more difficult than the seal P2.Therefore, can be taken to change the flow direction, P1 in the stem end to P2 at the stem end, which is high pressure, Large sanitary check valves are more effective, such as bellows valves that should normally be considered for sealing P2.

5) Using lens pad sealing method
For the seal of the upper and lower covers, the valve seat and the upper and lower valve body seal. If the plane seal, under high temperature and high pressure, poor sealing, causing leakage, you can use the lens pad seal, can get satisfactory results.

6) Replacing the gasket
So far, most of the gasket is still using asbestos board, at high temperatures, poor sealing performance, life is short, causing leakage. In this case, you can use the winding gasket, “O” ring, now many plants have been used sanitary valves.

Read More