How to automate an existing manual valve
Sometimes process requirements change and it becomes necessary to replace an existing manual process valve with an automated on/off or control valve. Instead of pulling the old valve out of service and replacing it with a new valve, users should consider automating the existing valve. If the valve is in good condition and has the means to mount an actuator, automating it can save time and money.
The preferred method is to remove the valve from the line and automate it in the maintenance shop, but that is not always possible. If you choose to automate the existing valve inline, make sure the valve is not under pressure and follow the plant’s lockout tagout (LOTO) procedures before working on the valve.
Know what you’re working with
To start, identify the size, make, and model of the valve. Consult the valve manufacturer’s literature or consult with a manufacturer’s representative for the torque (rotary valves) or thrust (linear valves) requirement of the valve. Ask the manufacturer or the representative if it is recommended to automate the valve.
Make sure the valve has an actuator mounting pad or body bolts that can be used to mount the actuator without compromising the integrity of the valve. Most modern ball valves have pre-drilled mounting holes for actuation (see Figure 1). If using body bolts to mount the actuator, make sure the bolts are long enough to engage the bracket and valve body when they are reinstalled. Ask the valve manufacturer for its recommendations for length and grade of bolts if existing bolts need to be replaced (see Figure 2).
Selecting an actuator
Determine the additional safety factor you want to add to the manufacturer’s recommended torque and add it to the manufacturer’s torque. This safety factor will ensure the valve will operate even if the air supply drops slightly or if the mounting kit binds slightly and increases the required torque. Also, as an actuator wears and air bypasses the pistons, the torque output will start to decrease.
Determine the desired function of the actuator and make sure it is the proper size. After choosing an actuator, consult with the valve manufacturer or rep and obtain the proper mounting kit to adapt the actuator to the valve. Please note, there are custom bracket manufacturers that will adapt just about any brand actuator to just about any brand valve so don’t worry if the valve and the actuator are different name brands (see Figure 3). The important thing is to make sure you are using a rotary actuator on rotary valves and linear actuators on linear valves. The actuator supplier can help obtain the correct mounting kits in most instances.
Before installing the actuator, make sure the valve position matches the actuator. If the actuator is a fail-closed actuator, make sure the valve is in the closed position. When an actuator is mounted on a rotary valve, leave the mounting bolts slightly loose and stroke the actuator a couple of times. This will ensure the mounting bracket is properly aligned and is not binding.
Torque the bolts to the proper tightness. After the bolts are tightened, stroke the actuator fully open and fully closed a few more times to make sure nothing is binding and the valve opens and closes smoothly. Most linear valves and actuators use a two-piece stem coupling (clamshell coupling). The linear actuator will include a yoke that attaches to the valve. Some linear actuators require the user to add low-pressure air to slightly open the actuator before attaching the stem clamshell (see Figure 4). This will preload thrust to hold the valve tightly in the closed position. Consult the valve and actuator manufacturer.
Finally, add any controls such as solenoids, limit switches, or positioners to the assembly if they are needed. Attach it to the plant air and wiring and test one more time before returning the valve to service.
Ronnie Moore is resident valve expert working in inside sales and support at Cross Co, a CFE Media content partner. This article originally appeared on Cross Co’s process instrumentation and valve blog. Edited by Jack Smith, content manager, Control Engineering, CFE Media, firstname.lastname@example.org
KEYWORDS: process actuator, automated control valve
- If the valve is in good condition and it has the means to mount an actuator, you can save time and money by automating it.
- Determine the additional safety factor you want to add to the manufacturer’s recommended torque and add it to manufacturer’s torque.
- Before installing the actuator, make sure the valve position matches the actuator.
Can your plant save time and reduce costs by automating existing valves instead of replacing them?