Forces Required to Close Pinch Valves at High Pressures.
There are an increasing number of pinch valves being supplied for high pressure slurry applications.
Corflex believe that in the interest of safety Engineers should be made as fully aware as possible of the forces required to not only close pinch valves but to ensure that they do not leak when closed.
Corflex has been building Pinch Valves since 1981 and can safely claim that it supplies Pinch Valves for higher pressures than any other similar valve. Over the years Corflex has conducted many tests on different size pinch valves to ascertain the actual force required to close and seal pinch valves of different sizes at different pressures.
There are no National or International Standards on the design or strengths of pinch valves as there are with many other type of valves.
PINCH VALVE SLEEVE
The strength of a pinch valve sleeve is dependent on the reinforcement used in its construction. The most suitable type flange is what is known as a cuff flange as opposed to a full face flange.
Below is a photograph of two cutaway sections of the Corflex Pinch Valve Sleeves.
The one on the right is for relative high pressure applications; it is reinforced with 2 or 4 ply of steel wire depending on pressure required.
The one on the left has 4 ply of much larger size wire, which is used for very much higher pressure applications.
A pinch valve sleeve is basically a rubber hose and similar standards to those in quality hose manufacture should apply. The industry standard is 4:1 burst pressure to working pressure with a test pressure of 2:1. High pressure pinch valves have enclosed bodies so the ratio can be reduced to 3:1with a test pressure of 2:1. This should be the minimum standard for safe working pressures.
Pinch Valve Sleeves when closed take a shape similar to the drawing below. With other valves such as plug, ball or gate there is little or no force trying to open the valve. With Pinch Valves apart from pressure trying to move the rubber out of the way, there is also an all round force trying to open the valve. Pinch Valves when closed may look shut but when pipeline pressure is applied they will leak unless there is sufficient force on the sleeve.
The most common reason for pinch valve failure is usually the valve leaking when closed.
PINCH VALVE BODIES AND CLOSING MECHANISMS
Pinch Valve enclosed bodies should not only be strong enough to support the pincher mechanism but strong enough to contain the valve sleeve test pressure in the event of a sleeve failure.
The forces required to close and seal pinch valves are very high and increases greatly with size and pressure. The only practical way to operate them at high pressure is hydraulically.
Traditionally pinch valves usually have rising actuators as this is less expensive than alternative methods.
These two nuts take the full force of the closing mechanism or the force trying to open the valve (See drawing below)
The high forces required to close pinch valves will generally greatly exceed the safe working load of the nuts.
Forces to close and seal
The sealing tests that Corflex conducted are to American Petroleum Institute Standard 598 as per the drawing below.
Force required to close and seal Corflex Pinch Valves.
| Size | 10 Bar | 16 Bar | 25 Bar | 40 Bar |
| 250mm | 13 Tons | 18 Tons | 27 Tons | 39 Tons |
| 300mm | 17 Tons | 24 Tons | 34 Tons | 51 Tons |
| 350mm | 23 Tons | 34 Tons | 49 Tons | 73 Tons |
| 450mm | 35 Tons | 51 Tons | 77 Tons | 115 Tons |
| 500mm | 41 Tons | 61 Tons | 88 Tons |
These tests were conducted on different standard sizes from zero pressure upwards in one Bar increments. From this Corflex were able to draw curves for each size valve for all pressures.
Some of the tests were done on different sleeves of the same size with similar results.
There is no reason to suppose that similar valves will not require similar force.
To ensure the valves do not leak a minimum of 10% should be added to the forces and preferably more.
Corflex had to design their valve to handle these forces. This meant that the valve could not have a rising actuator as it could be considered unsafe.
Below is a drawing showing the valve is closed from both sides with the hydraulic cylinders firmly attached to the valve body using 4 x large diameter Hi-Tensile Bolts.
With the high forces involved, Pinch Valves must be built to ensure the safety of personnel as well as efficient operation.
It is possible to build pinch valve sleeves for much higher pressures but the force required to seal would start to damage the sleeve.
Corflex has found from practical experience that the maximum force that should be applied to their sleeves is 120 Tons on large diameter valves.
For force required to seal other size pinch valves at different pressures contact Corflex Engineering.
Corflex suggest witnessed testing to API 598 for all high pressure pinch valves.