We Don’t (Usually) Register Actuators
File:PVE-4711, Last Updated: Dec 3/2010, By: LB
We often get asked to register valve actuators, but usually we don’t do it for a couple of reasons…
It is not possible to get many actuator designs to pass the ASME code rules which would be required for registration. For starters, picture this actuator being redesigned to use B16.5 flanges instead of its stamped steel flanges integrated into the housing. Not that there is anything wrong with this type of design, but if it was designed to code rules, the flanges (and other components) would weigh much more.
There is a class of actuator that has the piping system pressure on one side of the diaphragm. These actuators do need to be registered, which means that the actuators need to pass code rules.
Some valves have built in regulators where the housing for the regulator is the same part as the valve body. The stresses from the regulator need to be included with the stresses from the valve when the this type of valve is analyzed.
ASME VIII-1 – the bible of pressure vessel design – states this about the design of actuators:
U-l(c)(2) Based on the Committee’s consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel [or actuator] which meets all the applicable requirements of this Division may be stamped with the Code U Symbol:
U-l(c)(2)(c) pressure containers which are integral parts or components of rotating or reciprocating mechanical devices, such as pumps, compressors, turbines, generators, engines, and hydraulic or pneumatic cylinders where the primary design considerations and/or stresses are derived from the functional requirements of the device;
Or to paraphrase ASME – you can use pressure vessel rules to design valve actuators if you want, but because the primary loading is from the force on the valve stem, the use of only code rules in the design of actuators will probably not be adequate.
Most actuators on a valves are not part of the piping system for the fluid that the valve is regulating. Instead they are part of the instrumentation piping system. These piping systems are usually small diameter and contain air. Each province has its own piping rules, but most do not require registration of small diameter air piping systems. For example in Ontario any air line 3/4″ diameter or less does not need registering. (See piping charts for all provinces here ). An actuator is a fitting attached to a line and a fitting does not need registration if the line that feeds it does not need registration. Similar exemptions usually can be found for hydraulic actuators.
There will always be exceptions, occasionally your actuator will need registering, but most of the time it will not. Also, the valve might still need registering even if the actuator does not.