# What Is The Formula For The Coefficient Of Friction Top 10 Problems When Using Regulating Valves

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## Top 10 Problems When Using Regulating Valves

1. Why does a two-seat valve tend to oscillate when operating under small opening conditions?

In one-way valves, when the medium is open-flow type, they are stable. When the medium is a closed flow, it is unstable. There are two valve arms on a two-seat valve. The lower core is in the flow-closed state while the upper core is in the open state. In this case, under small opening conditions, the closed type of valve core will easily cause valve oscillation. That is why two seat valves can be used for small opening conditions.

2. Why are double-seal valves not used as sanitary shut-offs?

The two-seat valve core has the advantage of the power adjustment of the double-seal valve, allowing for a large pressure difference. And its failure is that the two sealing parts cannot be in good contact at the same time, which causes large leakage. If it is used purposefully and forcibly in closed situations, the result will not be good, even if there are many improvements made to it. (such as a double-seal sleeve valve)

3. Why is the purge control valve stroke ineffective and the rotary control valve prevent clogging?

The core of the valve stroke is vertical throttle, but the medium flow direction is horizontal. So there must be many twists and turns in the valve flow path, making the valve flow paths very difficult. Therefore, there are many blind spots that provide space for centralization, which over time causes blockages. The throttle direction of the rotary stroke valve is straight, the medium flows in and out, which can easily absorb the impure medium. At present, the flow path is simple, and there is a small place for intermediate placement, so the rotary stroke valve has a good anti-blocking function.

4. Why is the stem of a direct control valve thin?

It involves a simple mechanical principle: the greater the sliding friction, the less the rolling friction. The straight stroke valve stem moves up and down. If the mixture was pressed too slowly, it would wrap the stem tightly, resulting in a large hysteresis. So far, the valve body has been designed to be small and thin and the filling has used PTFE with a small coefficient of friction in order to reduce hysteresis. But the problem that arises from this is that the rare valve stem is easy to bend and stuffing has a short service life. To solve the problem, the best way is to use a rotary valve stem, a control valve like a rotary stroke. Its valve stem is 2 to 3 times thicker than that of a straight valve. And it uses graphite inserts with long service life. The stiffness of the valve stem is good, the service life of the plug is long, the friction torque and hysteresis are rather small.

5. Why does a rotary stroke valve have a large closing pressure difference?

This is because the torque on the rotating shaft produced by the force between the center of the valve or the valve plate is very small.

6. Why is the desalination service life shorter when using a fluorine rubber diaphragm butterfly valve?

The volume of desalinated water contains low concentrations of acids or alkalis, which are highly corrosive to rubber. Corrosion of rubber is characterized by increased wear and tear and low strength. The negative effect of using a rubber butterfly valve and a diaphragm valve is actually due to the rubber’s corrosion resistance. The rear rubber diaphragm valve is upgraded to a corrosion resistant fluorine diaphragm valve. But the diaphragm of the fluorine diaphragm with the diaphragm valve can not withstand being folded up and down and broken, resulting in mechanical damage and a short service life of the valve. Now the best way is to use water treatment special ball valves, which can be used for 5 to 8 years.

7. Why should shut-off valves try to use tight seals?

Sanitary shut-off valves require leakage to be as low as possible. The leakage of the soft sealing valve is the lowest, so the sealing effect is definitely good. But it is not old, it is not reliable. Given the double standards of minimal leakage and reliable sealing, soft sealing is not the same as hard sealing. Take the control valve with ultra-light full, for example, sealed and filled with a stable alloy for protection, reliable, has a leakage ratio of 10 to 7, everything that has already met the requirements of shut-off valves.

8. Why are sleeve valves replacing single seat and double seat?

Sleeve caps, which first appeared in the ’60s, were widely used in the ’70s around the world. Sleeve valves made up a large percentage of petrochemical equipment imported during the ’80s. At that time, many people thought that sleeve valves could replace the single seat and double seat to become a second generation product. So far, that is not the case. Single seat valves, double seat valves and sleeve valves are used equally. Because sleeve valves only improve throttle response, they have better stability and maintenance than a single seat. But its weight, anti-blocking and leakage index are the same as those of single seat and valve-seat-seat.

9. Why is choice more important than counting?

Compare calculation and selection, selection is more important and complex. The calculation is just a simple formula. It is not the formula itself, but the accuracy of the given parameters that is important. Selection involves many factors, carelessness will lead to inappropriate selection, which not only wastes labor, material, and money, but the results of use are not good, causing many problems in use. such as reliability, service life and quality, etc.

10. Why is the piston actuator used more in air valves?

In pneumatic valves, the piston actuator can fully utilize the air pressure to make the size of the actuator smaller than that of the film type. The pressure is great. The O-ring on the piston is also more reliable than the film. Overall, it is becoming more and more popular.

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