Omni Instrumentation & Electrical Services, Inc., had installed several hundred control valves as part of a large process control project, as per design and specification. But when commissioning commenced using water batch testing and product in the lines, a severe pipe hammer problem was quickly noted, shaking and moving piping on racks and risers, sometimes violently. A solution was needed, and fast, to prevent damage and worker injury.
The control valves were a mixture of stainless-steel butterfly and full-port ball valves with sanitary fittings ranging from 1.5” to 5”. The valves were discrete (on/off) fail-close, pneumatically-powered with a maximum pressure of 150 psi, and actuated by a 24V DC solenoid valve. There were also limit switches to determine open and closed. The valves were controlled by an I/O-based central process control system, and the air provided to the valves was approximately 100 psi.
Omni determined that the hammer problem stemmed from the control valves closing too abruptly. The solution would be to slow the valves’ closing time from less than one second to between 4-5 seconds to slow down air release and gently close them against the moving fluid. This could be accomplished by installing high-quality, adjustable, repeatable, lockable pneumatic flow restrictors that could be adjusted across a range on all valve exhaust ports.
We located a restrictor design that would meet these criteria and ordered several dozen for testing by the commissioning team. The flow restrictors were installed by Omni technicians and set to provide a 5-second valve closing time, allowing the valve to seat properly on the closed limit switch. A 10-second delay was programmed on the process controls side to allow the valves to close fully before triggering an alarm. Once it had been verified that the restrictors had corrected the problem where installed, the remaining restrictors were overnighted to the facility. Omni had several of our instrument technicians working ahead, installing and testing each valve on specific systems that were ready for commissioning.
The flow restrictors did the trick and the problem was resolved in short measure.
Omni Instrumentation & Electrical Services, Inc., located in New Jersey and Maryland, is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation & Electrical Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.