REPORT ON A SEALING TEST OF 3 x 500 ∅ HIGH PRESSURE CORFLEX PINCH VALVES
Introduction
Corflex Engineering (Pty) Ltd manufactures pinch valves, primarily for the mining and minerals processing industries.
This sealing test was at the customer's request. In so far as Corflex is aware there has never been a sealing test as per the following one by any other Pinch Valve Manufacturer Worldwide for a sealing test of a 500mm pinch valve at 27, 5 Bar.
Standard Employed
In so far as it is applicable to this type of valve, API 598 was adopted as the reference standard. In particular, the sections "high pressure closing test" and "maximum allowable leakage rates" were used as being the most appropriate indicators of successful valve operation and sealing.
Description of the Valve
A pinch valve is basically a rubber hose or sleeve which is clamped in a pipeline and pinched or squeezed together to stop or control flow, normally a fluid and often a slurry mixture of carrier fluid and solids.
The sleeve is contained and supported in a body frame, which frame carries and supports the closing mechanism, which is vice-like, having the pinchers acting on the centre line of the sleeve.
The sleeve in a High Pressure valve is typically hand constructed from rubber with steel cord reinforcement. It is generally lined internally with a layer of natural rubber to provide additional abrasion resistance, in this case Neoprene was used.
The pinching mechanism is hydraulically actuated and the valve is fitted with four trunnion mounted non-rising hydraulic cylinders each cylinder secured by four high tensile cap screws. The use of rising actuators fastened with two nuts onto the tie bars is not suitable due to the high forces required to close the valve and the potential danger of shearing the nuts. The use of rising actuators should be restricted to low pressure applications for safety reasons.
It must be noted, that the sleeve, and therefore the fluid, is completely isolated from the body of the valve and the closing pinchers. There is no penetration of the sleeve by spindles, operators, etc.
The Test Rig
This is shown above and comprises of the valve, the hydraulic power pack, and the pressurising hand pump. The fluid used was potable water.
The up-stream flange was fitted with an inlet hose at the 'top' of the sleeve where it meets the flange, and able to be pressurised via the hand pump. A pressure gauge and safety relief valve was fitted on the centreline of the flange.
The down-stream flange was similarly fitted with a pressure gauge and relief valve. The outlet in this case, also at the 'top' of the sleeve, was an up-stand of hp pipe so that any leakage (droplets of fluid) could be observed.
The Test Procedure
- The valve (open) was filled with potable water and pressurised to a nominal 8 bar to fully expel any residual air and to provide a back-pressure to the closing mechanism so that the sleeve could be pinched in as normal an operating manner as possible.
- The hydraulic pressure was applied and the valve was fully closed.
- The up-stream side was then pressurised to 27,5 Bar
- The down-stream side was exhausted to zero pressure via the stand-pipe.
- Leakage across the 'seat' was observed as a droplet of water exiting the stand-pipe.
Observations
Leakage was observed as a droplet of water forming on, and falling from, the stand-pipe.
In this period, the up-stream pressure did not reduce.
The test was repeated with all three valves and the same results observed.