Actuator Mounting Tips – Ball Valves
February 21st, 2019 by Amanda Schumann
When mounting a pneumatic or hydraulic actuator with a bracket and adaptor to a quarter turn valve stem, careful consideration needs to be given to the adaptor coupling. It is typical with gland packed valves but also with non gland packed valves to have a bracket and an adaptor coupling between the actuator and the valve as direct mounting is quite often not possible, either because the gland packing area needs to be accessed for adjustment or because of the size of the valve in relation to the actuator or because there is no through bolt flanged raised mount pad. An enclosed or open bracket are both possible, smaller process valves of course can be direct mounted and although this prevents access to the gland packing, direct mount valves like APV include Belleville washer arrangement that removes the requirement to adjust the gland packing. Of course most oil and gas end users would rather have the option of being able to access the gland packing area for adjustment should it be required and also have greater visibility of any stem leakage should it occur. Sferova, Starline & APV floating and trunnion ball valves in 600 class and higher have triple barrier stem sealing so access to the stem area is not required, hence direct mount or an enclosed bracket is possible.
Consequently, there are many beginners traps in mounting an actuator to a valve even with the lighter, compact alloy case rack and pinion style actuators made by major manufacturers such as Air Torque (heavy wall all Alloy case). These actuators are much lighter and also have a much more balanced, centred strain on the stem area (Balanced double rack & pinion). This style is proving more popular in oil and gas applications as brands like Air Torque are now SIL 3 certified and ‘EX’ rated. For more information on Air Torque actuators click here.
Also see our previous post on using compact rack and pinion actuators in lieu of scotch yoke, piston style actuators click here.
Irrespective of whether you are using a compact rack & pinion or a heavy duty or a heavy duty scotch yoke piston style actuator, enormous forces can be exerted on the valve stem area. This particularly applies with heavy duty piston Biffi/Bettis/Actreg/Torqturn style scotch yoke cylindrical heavy duty actuators. Not only because they cover such large torque ranges but also because there is an enormous torque on the stem. Any side loading of the stem can very quickly cause stem leakage if the actuator is not mounted centrally or if over time the bracket and adaptor start to slightly bend. Even with a misalignment of .3mm, the stem will eventually start to leak. Consequently, great care must be given to ensure a heavy duty or/and high tensile bracket and adaptor is selected and in addition extra support and stiffening of the actuator weight maybe required as enormous forces are exerted on the stem area, particularly during the emergency shutdown spring closing stroke which can be as fast as one second. Naturally the bracket needs to be heavy duty steel plus zinc plating and the bolts need to be anti-corrosive high tensile with spring washers. For the adaptor/ coupling, whilst 304 and 316 may be acceptable in smaller sizes in low torque actuators, even in these sizes GSL stocks 303 high tensile Italian made, other acceptable materials are 17-4, S31803, Nitronic 50 etc. In large sizes 410, 4130 or 4140 zinc plated or if sufficiently heavy duty in design then A105 forged and zinc plated can also be used. Also remember that if fitting a declutchable gearbox between the actuator and the valve this can make centralising and alignment even more difficult to perfect and the coupling/adaptor will also increase torque slightly.
Tip (1) – Before testing actuator remove any synthetic oil from ball/ seat as some manufacturers squirt into the sealant injection line as a light corrosion inhibitor but during storage it hardens and increases torque.
Tip (2) – The tiniest bit of debris in the line at start up or beyond can turn your seat into a ‘break shoe’, ramping the torque up to 250% higher! Since safety factors are only 50-200% this can make the valve impossible to stroke, particularly if it has not been operated for a few months. Also moving the valve with debris accumulated on or in front of the seat can then damage the soft seat insert. See our post on Actuator Sizing click here.
Also click here to see the Australian Pipeline Valve IOM on the APV Trunnion Ball Valves and APV-Torqturn actuators which includes service information in flushing seat area before stroking, seat types, and regularly ‘exercising’ actuated valves.
Also see our technical publication on ball valve seat materials click here. Applying sealant injection to the seat area of trunnion mount ball valves can reduce torque by 50% (but then the grease can attract debris that can damage the seat when turned). The seal injection points can also be flushed to try clear grease. Click here for our post on Maintaining & Servicing Trunnion Ball Valves.
Tip (3) – Global Supply Line Engineering can do an actual torque test on the valve and the actuator. Also we are approved to do Factory Acceptance Test (FAT) on the complete actuated valve, whilst under full differential pressure and with only minimum allowable air supply (after the controls are fitted through the reduced orifice of the air inlet valve). Even then, this only simulates a test with perfectly clean water but we can also simulate dry gas service with our high pressure Nitrogen test facility. If needed the valve can be submerged tank tested during stroking to prove no stem area leakage during stroking.
Global Supply Line also keep large stocks of genuine Air Torque 100% European made integral (not welded) high tensile stainless steel brackets in smaller sizes and carbon steel polyester coated brackets in medium sizes to suit our large stock of Air Torque compact rack & pinion actuators. For larger size heavy duty actuators we custom manufacture heavy wall, rectangular, heavy duty brackets and zinc plate. We also keep large stocks of declutchable gearboxes in multi-turn and quarter turn APV-Diamond gear brand.
We keep large stocks of square and double square 303 stainless steel high tensile ‘reductions’ to suit insertion into compact rack and pinion actuators to allow direct mounting. In addition we keep semi-machined 303 stainless steel semi un-machined Italian made adaptors that we can machine to suit adaption between valve and actuator for bracketed assemblies.
Our in-house automation facility is fully approved by all manufacturers that we represent such as Starline/ Air Torque/ Sferova/ JC/APV, etc. to supply & fit, automate, test and accessorise full control and automation packages. We can supply and fit any brand of actuators such as Bettis/ Actreg/ Rotork/ APV-Torqturn etc. and keep large stocks. Not only rack and pinion Air Torque actuators but also heavy duty compact scotch yoke piston actuators in APV, Torqturn and Biffi (Emerson) HD. See our full stock list at our website click here.
We now stock Actreg and Biffi scotch yoke series up to 30,000NM.