Which valves require flow direction selection? How?
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Release Time：2021-05-21
Single-seal control valves such as single-seat valves, high-pressure valves, and single-seal sleeve valves without balancing holes need to be selected for flow direction. Flow open, flow closed each have advantages and disadvantages. Flow open type valve work is relatively stable, but the self-cleaning performance and sealing performance is poor, short life; flow closed type valve life is long, self-cleaning performance and sealing is good, but when the stem diameter is less than the valve core diameter stability is poor. Single-seat valve, small flow valve and single-seal sleeve valve are usually open and closed when flushing is severe or self-cleaning is required. Two-position type quick-opening characteristic regulating valve selects flow closing type.
What are the seven steps to determine the caliber of a regulating valve?
1) Determine the calculated flow rate -- Qmax, Qmin2) Determine the calculated pressure difference-select the resistance ratio S value according to the system characteristics, and then determine the calculated (when the valve is fully open) pressure difference; 3) Calculate flow coefficient-select appropriate calculation formula chart or software to find max and min of KV; 4)KV value selection-according to the max value of KV, the primary caliber is obtained; 5) opening checking calculation-no more than 90% valve opening when Qmax is required; Qmin ≮ 10% valve opening; 6) actual adjustable ratio checking-general requirements shall be ≮ 10;R actual> R requirements 7) caliber determination-if unqualified, reselect KV value and verify again.
Why the shut-off valve should try to use hard seal?
The cut-off valve requires the lower the leakage, the better. The leakage of the soft seal valve is the lowest. The cut-off effect is of course good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage, sealing and reliable, soft seal cut off is not as good as hard seal cut off. Such as full-featured ultra-light control valve, sealed and piled with wear-resistant alloy protection, high reliability, leakage rate of 10~7, has been able to meet the requirements of the shut-off valve.
Which valves require flow direction selection? How?
Single-seal control valves such as single-seat valves, high-pressure valves, and single-seal sleeve valves without balancing holes need to be selected for flow direction. Flow open, flow closed each have advantages and disadvantages. Flow open type valve work is relatively stable, but the self-cleaning performance and sealing performance is poor, short life; flow closed type valve life is long, self-cleaning performance and sealing is good, but when the stem diameter is less than the valve core diameter stability is poor. Single-seat valve, small flow valve and single-seal sleeve valve are usually open and closed when flushing is severe or self-cleaning is required. Two-position type quick-opening characteristic regulating valve selects flow closing type.
Why is the stem of the straight stroke regulating valve thinner?
It involves a simple mechanical principle: large sliding friction and small rolling friction. Straight travel valve stem up and down movement, packing a little tight, it will be the stem wrapped very tight, resulting in a larger return. For this reason, the valve stem is designed to be very small, and the filler is often used to have a small coefficient of friction to reduce the backwardness. However, the problem caused by this is that the valve stem is thin, which is easy to bend and the filler life is short. To solve this problem, the best way is to use the travel valve stem, that is, the angle stroke type of regulating valve, its stem is 2 to 3 times thicker than the straight stroke valve stem, and the use of long-life graphite packing, stem stiffness Good, long packing life, the friction torque is small, the return difference is small.
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