Hydratron Relief Valve Test Rig – Case Study
Hydratron, part of Pryme Group, manufacture high pressure and flow control equipment, and are widely recognised for creating innovative solutions that provide performance assurance. They were approached by a global valve manufacturer looking to increase their production capacity through improvements to their testing through a new relief valve testing system. Hydratron designed and manufactured a bespoke valve test rig to run pressure tests on their relief valves that would be capable of high-volume gas ‘pop’ testing and lower-pressure gas back-pressure testing.
Engineering a custom valve test solution
The testing system that Hydratron were designing would have many important design considerations:
Test Requirements of Relief Valves
A diverse range of valves would be under test, including ½” to 8” flanged valves and ½” to 2” screwed valves. The testing pressures would need to go up to 6,500psi Water, 6,500psi Gas (pop test) and 800psi Gas (back pressure).
User controls and safety measures
With the high energy involved, safety interlocks were crucial; they would ensure test pressure on any of the lines could not be induced until enough clamp pressure was applied to the valve on test and the enclosure doors are closed. Ensuring clamps could not be released and the test enclosure doors remain locked when test pressure is present was an important safety feature.
A touchscreen interface would be included to manage the control of the system. This would allow the operator to enter the size and pressure of valve they are to test, provide indications of clamp and test pressures and manage all the interlocks. It would also allow for a blow down function to purge the system of water after a water test, prior to a gas test.
Relief Valve Test Rig Design Challenges
By working closely with the customer, Hydratron identified the main design challenges as follows:
Bore size to achieve the ‘pop’ of the valves
Hydratron researched similar systems and current test methods on the customer’s existing rig to determine the bore size. Pressure rating was a given a lot of attention in the design; too large and it would be more unlikely to be suitable for the 6,500psi pressure. 1 1/2” stainless steel pipe was chosen for the final valve testing system.
Valves to maintain the bore size, rated to the working pressure
Hydratron initially identified valves for use in the valve testing system, but upon further investigation, these actuated ball valves opened rapidly. This raised concerns about potential side-loading of the valves when acting against pressure. Furthermore, to achieve the pressure, these valves could only be supplied with weld type ends, not screwed.
Designing the safety interlock system
Using this pipe, the typical Hydratron circuitry design which controls the safety interlock to stop test pressure being induced, and vent it from the test piece, was unsuitable. They overcame this by redesigning the circuitry to include multiple pilot-operated 2 position, 2-way valves located to achieve the same result.
Ensuring effective air blow down function
Air entering the system pipework and venting out of the system pipework needed to be controlled carefully to reduce the risk of it not working and purging the lines of water.
Charging the accumulator and vessels
Due to the large nature of the accumulator and vessels, Hydratron had to utilise a liquid pump and gas booster respectively, each with a high enough performance to charge the accumulator and vessel in an acceptable time frame. This involved assessing flow rates at different pressures and resulted the installation of higher specification Hydratron pumps than typical supply.
Other design considerations
The unit would have to fit in an existing location, and therefore be no wider than 2,500mm. Rear access for the valve and maintenance was also required.
Relief valve testing rig – designing the solution
The customer reviewed the detailed technical proposal and specification, and they were happy to instruct Hydratron to proceed with the construction of the bespoke relief valve testing system. Throughout the design and build process, Hydratron were in frequent contact with the customer to ensure that the best relief valve testing system for their needs was produced.
The hydraulic system utilised a fluid tank, an air operated liquid pump, a large 35 litre accumulator, valves and instrumentation. The gas line used direct large bore to the test piece to allow a high release of energy to be applied. The gas pop test system necessitated a gas booster, a large 50 litre vessel, valves and instrumentation. A gas reducing regulator, valves, and instrumentation were installed for the Gas back pressure test system.
Additional design considerations
Layout and access
The accumulator and vessel were oriented vertically to create space at the rear of the unit. The layout was designed to allow for a rear door for access to the valve as well as access to the rear panels of the unit for maintenance.
Maintaining ergonomics with a larger tank
A key design challenge that the engineers at Hydratron resolved was how to fit a larger fluid tank and more panel controls into similar size footprint as existing benches, as well as making way for the welded pipework. The tank and test table were raised which reduced the footprint. A clever layout of the control panel allowed the fitting of a multitude of controls.
Test flanges to suit a larger bore
It was challenging to get the test flanges designed to suit all the valve sizes, particularly when stepping down for the seals of smaller valves and withstand the pressures involved in testing. Hydratron produced a solution involving the use of a larger O-ring bore seal.
Programming and Electrical Control
The nature of the multiple features in this test bench required a comprehensive touch screen interface. Hydratron developed a single screen touchscreen programme for ease of operation. This was highly detailed, including lists of all valves, many different valves for test and clamp pressures.
Improved clamp pressure setting
Hydratron developed a formula-based approach to the clamp pressure calculation based on the size of valve and test pressure to be induced. This is usually done by set values to cover a range of test pressures, however this new approach suggests optimum clamp pressures, simplifies the program in the longer term and reduces the likelihood of mistakes due to removing manual entries.
If you would like to find out more about this custom designed, relief valve test rig, including a video of it in action, you can view the full write-up on the Hydratron website.