By HY Valves

Valve FAQ

  1. Why can’t the double seal valve be used as a shut-off valve?

The advantage of the double-seat valve spool is the force-balanced structure, which allows a large pressure difference, and its prominent disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is used artificially and compulsorily for cut-off occasions, it will obviously not work well. Even if many improvements are made for it (such as double-sealed sleeve valve), it is not desirable.

  1. Why the double-seat valve is easy to oscillate when the valve is working at a small opening?

For a single core, when the medium is a flow-open type, the ball valve stability is good; when the medium is a flow-closed type, the valve stability is poor. The double-seat valve has two spools, the lower spool is in the flow closure, and the upper spool is in the flow opening. In this way, when working with a small opening, the flow-spool type spool will easily cause the valve to vibrate. The reason why it cannot be used for small openings.

  1. What straight-line control valve has poor anti-blocking performance, and angular travel valve has good anti-blocking performance?

Straight stroke valve spool is vertically throttled, and the medium is flowed in and out horizontally. The flow path in the valve cavity must be turned upside down, which makes the valve’s flow path quite complicated (like an inverted S-shape). In this way, there are many dead zones, which provide space for the precipitation of the medium, which will cause clogging if it continues for a long time. The direction of the angle travel valve is the horizontal direction. The medium flows in horizontally and flows out horizontally. It is easy to take away the dirty media. At the same time, the flow path is simple and there is little space for the medium to settle.

  1. Why is the cut-off pressure difference of the angular stroke valve large?

The cut-off pressure difference of the angular stroke type valve is large because the torque generated by the combined force of the medium on the valve core or the valve plate to the rotating shaft is very small, so it can withstand a large pressure difference.

by HY valves

Butterfly Valve

  1. Why is the straight stroke valve stem thinner?

It involves a simple mechanical principle: large sliding friction and low rolling friction. The stem of a straight-stroke valve moves up and down, and the packing is slightly compressed, and it will wrap the stem tightly, resulting in a large return difference. For this reason, the valve stem is designed to be very small, and the packing is usually a tetrafluoro packing with a small friction coefficient in order to reduce the backlash. The best way to solve this problem is to use a travel valve stem, which is an angle-stroke control valve. Its stem is 2 to 3 times thicker than a straight-stroke stem, and it uses a long-life graphite filler. The stem has good rigidity. , The filler has a long life, but its friction torque is small, and the return difference is small.

  1. Why do rubber-lined butterfly valves and fluorine-lined diaphragm valves have a short service life for desalinated water?

The desalinated water medium contains low concentrations of acids or alkalis, which are relatively corrosive to rubber. The corrosion of rubber manifests as swelling, aging, and low strength. The use of rubber-lined butterfly valves and diaphragm valves is poor. The essence is that rubber is not resistant to corrosion. The rear rubber-lined diaphragm valve is improved to a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve cannot be folded up and down, causing mechanical damage and shortening the valve’s life. The best way now is to use a special ball valve for water treatment, which can be used for 5 to 8 years.

  1. Why should we choose hard seal as the shut-off valve?

The lower the leakage required by the shut-off valve, the better. The leakage of the soft seal DIN globe valve is the lowest. Of course, the cut-off effect is good, but it is not wear-resistant and poor in reliability. From the double standards of small leakage and reliable sealing, the soft seal is not as good as the hard seal. Such as full-featured ultra-light control valve, sealed and stacked with wear-resistant alloy protection, high reliability, leakage rate of 10 to 7, has been able to meet the requirements of the shut-off valve.

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