What's this Maintenance Safety Bulletin about? All in-line flow-meters that are equipped with a ball valve for inducing an artificial load (to generate pressure). What's the problem? Under certain conditions the ball valve could unexpectedly shut off. If there is no relief valve in the circuit, it could cause a failure that could lead to severe injury, death, or substantial property damage. Tell me more! The majority of in-line flow-meters, especially those manufactured by Hedland® and Lake®, do not generally have load (pressure) generating capability. Accordingly, if a fluid power system cannot operate through a typical load cycle, it is usually not possible to obtain an accurate assessment of the pump condition - no pressure, no test! This problem is more apt to occur with hydraulic motors than it is with cylinders, because stalling a cylinder will generally cause the pressure to rise to the value of the pressure relief valve setting. Consequently, it is common for people to adapt either a ball valve or a needle valve to a flow-meter to facilitate artificial loading. A needle valve is acceptable because it restricts flow gradually. However, it is important to note that a relief valve MUST be in the circuit while using any type of valve that can restrict flow. The ball valve is undesirable because the dynamics of flow and pressure can cause it to close unexpectedly. This usually occurs at higher pressures. If a person were to use a ball valve (designed primarily as an on/off valve) to restrict flow there is a high probability that it will self-close at high pressure, leaving the person highly susceptible to a severe safety hazard. What immediate action must I take? If you have any flow-meters, regardless of brand or type, that are equipped with a ball valve rather than a needle valve (that do not have an integral safety relief valve) tag it/them out of use, and remove the ball valve(s) immediately. Replace the ball valve with a needle valve. Make certain that the needle valve is rated for the correct flow and pressure. If you are not sure, contact your fluid power supplier, or contact the flow-meter manufacturer. WARNING: All testing of fluid power systems and/or components MUST be conducted by trained, authorized personnel only. Failure to heed this warning can cause an accident that can lead to severe injury, death, or substantial property damage.

Waiver of Liability -

The Fluid Power Safety Institute™ does everything possible to ensure that the information and drawings contained in this safety notice are accurate, and the suggested procedures are deemed safe and reliable. However, these are general recommendations only and might not be applicable to all situations. You MUST have your engineering department in conjunction with your safety department read these recommendations and make the necessary changes for your application. The Fluid Power Safety Institute™ is not responsible for actions taken by untrained and/or unauthorized persons. Trained, authorized persons only should do ALL fluid power system service, repair, and troubleshooting.