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Pumps & Systems, September 2008
Have you ever looked at a valve, sluice or similar rotating equipment and wondered how to operate it?
In these days of limited maintenance coupled with reduced staffing levels, it is becoming increasingly difficult to find personnel with sufficient time to operate large multi-turn or difficult-to-turn valves and equipment in a timely manner. Some large valves are typically operated only once or twice a year during a plant shutdown situation, and often require the use of cheater bars (valve wrenches) with extension arms and a work crew to complete the task.
This manual operating procedure can take many hours and cost more in labor. Because of the high installation costs, the use of permanently installed actuators (actuator, control system and any associated power supplies) on these valves is often not an economic alternative for infrequently operated items.
Portable Valve Operating Technology Specifications
A possible answer to this problem is to use a one-man operated portable valve operating system (or valve exerciser), which can typically consist of a handheld continuous torque output driver, not an impact wrench. Commonly referred to as the "gun," this driver can be powered by either plant air (90- to 100-psi at 25- to 30-cfm), main electricity (120 to 220 VAC), battery electric (18 VDC) or a hydraulic power source (2000-psi, 4.75-gpm). With any of these power sources, it is possible to obtain guns that will produce in excess of 8,500-ft-lbs of torque that can then be utilized to turn valves or equipment when supplied complete with a mounting kit.
The mounting kit can be designed for permanent attachment to a valve in place of the operating handwheel / lever or alternatively can be supplied as a "clamp-on" type. The clamp can be attached to the existing valve handwheel/lever using bolts or U-bolts, allowing removal and relocation to another valve if required. Included in a well-designed mounting assembly is a safety "reaction arm," which attaches the gun to the valve body/adjacent equipment or steelwork.
This feature ensures that the gun does not spin should the valve stall or the valve stem stop turning during operation for any reason, minimizing the possibility of operator injury. Some handheld valve operators or exercisers currently require the operator(s) to become the reaction device with all the inherent dangers and injury possibilities involved (see Figure 1 for a typical operational situation).
By selecting a gun based on valve torque requirements and operating conditions, it is possible to operate almost any item with a rotating stem with speeds varying from a few RPM up to 65- to 70-rpm dependent on the torque output required from the gun. Speeds in excess of 65- to 70-rpm should be avoided, as most valves and gearboxes used with valves and manually operated equipment are not designed for high-speed operation.
The torque output from a gun is variable and controlled by different methods depending on the power source, usually a stepping clutch control system for electric units or raising/lowering the air pressure for pneumatic units. Each gun is supplied with a calibration graph or chart of power source against torque to assist with selection of the correct operating torque for an individual application.
As the gun-type units are light weight (a common maximum weight is in the range of 28- to 30-lbs), they can easily be moved, attached to another valve and connected to an adjacent power source to operate. This portability can be extended further with truck-mounted or transportable compressors for pneumatic versions or cab-mounted inverters for electric or battery units. With this flexibility, it is possible to operate equipment in remote locations, including along pipelines, within dams, at pumping stations, etc.
If the location involves operation in a hazardous or explosive area, only air-driven units can be used, as no other power source unit is approved for use within these areas. If other operational restrictive parameters require the operator to position himself away from the valve (with or without hazardous area considerations), remote control operation versions are available for operation up to 50-ft away from the equipment. These versions use either pendant-type pneumatic controls or an electrical control module.
Operation
Using pneumatic versions as an example, the method of operating a valve for the first time is to:
1) Securely attach the required mounting kit to the valve if it is not already installed.
2) Connect the pneumatic torque driver to the valve adaption using any supplied adaptors and location pins, ensuring that the reaction arm is correctly aligned and attached to the gun body.
3) Check that the supplied filter, regulator and lubricator unit (FRL) is filled with oil to lubricate the air motor and that an adequate air supply is available.
4) Set the air supply to the gun using the FRL to zero. If the operating torque required to turn a valve is known, proceed as A). If the torque is unknown, proceed as B).
A) Use the FRL regulator to set the required air pressure to produce this torque using the calibration chart supplied with the unit. Select the required rotation setting on the gun-forward or reverse-operate the control trigger to turn the gun on and rotate your valve.
B) Slowly increase the supply air pressure using the FRL regulator from zero during operation of the gun until the valve turns freely in a continuous manner. Once continuous operation is achieved, record this operational pressure for future reference, either on the valve body or in the maintenance record for the particular valve.
In addition to mounting directly onto the handwheel, gearbox or valve stem, extension arms, stem adaptors (AWWA or similar), offset gearboxes, indirect reaction arms, revolution counters and other system modifications can be supplied to suit different individual applications. In cases where a valve is inaccessible for direct operation, the use of a flexible, cable-driven drive system together with a torque driver can also be considered.
Martin West is sales manager (USA) for Smith Flow Control and has worked in the fields of valve locking for safety and valve drive systems for more than 20 years
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