Air lock free filling
Maintenance free evacuation system
CSV Test benches
A valve clamped horizontally can only be filled to the upper rim of its flange. In case of smaller or mid-size test benches, the outlet of the clamping unit is typically at the center axis of the outlet flange and water will only rise up this flange middle line creating a significant air lock inside that will cause two serious issues:
1) Extended test time The air lock will be pressurized to the same level like the high pressure testing water. Different to the mostly incompressible water the air compress significantly, leaving a larger volume to be filled by high pressure water. This water has to be supplied by the high pressure water pump that a rather poor filling performance. Consequently the time for increasing pressure inside a valve with an air lock takes several times longer compared to an evacuated valve.
2) Disguising the shell test result The effect on the shell test result is even more serious. The shell test will be evaluated based on the pressure drop appearing over the testing time. Because of water being mostly incompressible, the loss of a single drop of water from a completely filled valve will cause a serious pressure drop. That is how tiny leaks and cracks in the body are detected, even if you can not see the leak straight away. However, an air lock inside the valve will act like a spring or buffer. The volume lost via the water drop will lead to the air lock to expand by the same amount of volume. Because of the high compressibility of air, such a small expansion will not lead to any visible pressure drop and the slightly leaking valve appears to be tight.
Every METRUS control or shut of valve test bench is fitted with a fully maintenance free evacuation system, capable to create vacuum up to -0,9 bar inside the valve. With the test steps pre filling, evacuation and filling the valve will be free of air locks in shortest time avoiding test time extension and test result disguising completely. With METRUS maintenance free evacuation solutions, massive mechanical solutions to tilt the valve for filling are made obsolete.
BV Test benches
METRUS BV series test benches do have a vertical clamping unit. The upstream will naturally fill the valve to be tested to the upper rim. Consequently BV series test benches do not have an evacuation system within the standard scope of supply. However if valves to be tested have pockets or hollow spaces those might cause an air lock, leading to the problems described under “CSV”. In such case an evacuation system is the suitable solution.