Case Studies

Client Name: Daisho Sangyo Co. Ltd., Japan

Problem They faced:

Low Pressure closure test criteria is an optional feature for Check Valves. 

Japanese customers are very keen about finest performance of products having optional features included on to the product characteristics. Check valves is a self-operated valves that actuates with the pressure criteria. The piston disc tends to moves upward with the line pressure increases from inlet side, thus the flow passage gets open and the flow passes through, thereby inlet pressure tends to reduce and disc started returns back to its seating position resulting the inlet flow becomes stop.
On the contrary the outlet pressure start developing a counter pressure that push back the disc on to its seating position and the valve will become tight shut-off. Therefore the more the counter pressure develops, the chance of tight shut off is high. However in practical application check valve acts as a fuse in electrical circuit that tends to break/ isolate the line during pressure surge. So a check valve has to have the characteristic to crack down in low pressure and on the contrary shall stop back flow from outlet to inlet.
Therefore in the case of check valve/ non return valve demonstration tight shut-off seating at a low pressure is difficult to achieve than in high pressure. It requires proper design in place and high degree of manufacturing accuracy that will ensure self-actuated functioning and high degree of surface quality to reach to leak proof quality even when the counter pressure in low or even tends to zero.

Solution Provided:

We did a detail study on the product characteristics in order to adopt design change when our Japanese customer drew attention with this sophi feature. Firstly the disc design was converted to body guided which was earlier a cover guided design that often did not ensure the disc to return back to its factory fitted seating position leads to flow leak through back side.

It was then becomes a challenge to mitigate the smooth movement of disc up and down due to air tight situation. In order to counterfeit, several air pockets were crafted angular through out the perimeter in four quadrant and the movement of disc motion becomes smooth, repetitive and faultless.

The new designed check valve tested for seat tightness with air at a low pressure of 7 bar(g) [80 PSI(g)] in accordance with low pressure closure test of API 598/ ISO 12266 Part 1 standard and could achieve zero visible leakage though bubble test. The said valves were then tested with helium gas and the result repeats. This was needed to qualify the design for Cryogenic Applications as per design standard BS 6364.

Positive Impact after implementation: 

In general practice majority valve manufacturers are offering Check Valves with High Pressure Closure Test, because testing standard API 598/ ISO 12266 Part 1 specifies low pressure closure test an optional feature not a mandatory criteria.
With the previous design our valves also could not hold seat tightness at such low pressure and were usually tested high pressure closure test at a hydro test pressure of 110% of the designed line pressure.
With the design change we have standardised our Piston Check Valve design same for both common usage and cryogenic application. Characteristically our Check Valve is unlike the other similar products available in the market. The uncertainly factor in our Check Valve has come down to <5%.

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