Actuator Selection Process

Sizing Information

Choosing the correct actuator is as important as selecting the correct valve. The information offered below is presented in an effort to assist in the choice of the proper actuator for your application.

If you are unsure of your selection and feel you need assistance, do not hesitate to contact your local FLO-TORK representative or the FLO-TORK Corporate office.

Prior to beginning the actuator selection process it is necessary that you have the following information:

  1. The maximum torque required to break (unseat) the valve element from its fully closed (seated) position, against the maximum pressure differential.
  2. The maximum running torque required to operate the valve against the applicable flow rate and the differential pressure in the valve.
  3. The maximum torque required to seat the valve in its fully open position - (applicable for ball & plug valves).
  4. The maximum torque required to unseat the valve from its fully open position to start closing (applicable for ball & plug valves).
  5. The maximum torque required to close (seat) the valve in its fully closed position.
  6. The direction of operation required to close the valve - clockwise or counterclockwise. Normal assembly of the SERIES M scotch-yoke actuator is clockwise to close. NOTE: This is important as the SERIES M actuator is designed with a 5 degree torque plug cant that provides different output capacities at each end of stroke.

NOTE: Determine if the torque values provided include a sufficient safety factor for the application.

In addition to the torque data described above, the following application information is required to begin the selection process.

  1. What is the supply media to the actuator?
    1. Pneumatic
    2. Hydraulic - What type of hydraulic fluid is to be used?
  2. What are the minimum/maximum operating media supply pressures?
  3. Will the actuator be double acting or spring return?
  4. If a spring return stroke is required, is it fail open or fail close?

These guidelines are provided to assist in choosing the proper SERIES M scotch-yoke actuator using the data discussed above. The ACTUATOR SELECTION PROCESS listed below assumes a CLOCKWISE ROTATION TO CLOSE the valve and that the maximum torque requirement is to break (unseat) the valve element from its fully closed position. If these assumptions are incorrect, an alternate selection process must be used.

Actuator Selection Process

Double Acting Actuators

NOTE: FLO-TORK's SERIES M double acting torque charts are based on a clockwise rotation to close the valve. The torque charts provide start (break) torque values shown at 01, run torque values shown as minimum (min) and end (fully open) torque values shown at 900. Be sure that the maximum valve torque values at all positions of rotation are less than the minimum actuator output torque values.

  1. From the actuator torque charts select the pressure column that is equal to or less than the minimum operating pressure available.
  2. Move down the selected pressure column until you find a torque output that is equal to or exceeds the maximum break (unseating), run (dynamic) and fully open torque values of the valve.
  3. Move to the left in that line and determine the SERIES M model number in the model column.
  4. Now that the actuator has been selected, use the torque charts to verify that the maximum operating pressure does not exceed the maximum pressure rating of the actuator and that the output torque of the actuator does not exceed the allowable torque rating for the valve stem at the maximum operating pressure.

If either of these ratings are exceeded then the maximum operating pressure must be reduced (i.e. adding a pressure regulating valve) or an alternate actuator must be selected.

Spring Return Fail Close (CW) Actuators

NOTE: The SERIES M spring return torque charts are based on a clockwise spring stroke and provide the start (break), run (minimum) and end (closing) torque outputs for the spring stroke in addition to the pressure stroke output torques for the same positions of rotation.

The spring break torque (highest spring output torque) is shown at the 901 position. This corresponds with the lowest pressure stroke output torque which is also at the 901 position.

NOTE: The actuator output torque must exceed the maximum torque requirements of the valve at all positions for both the spring and the pressure strokes.

  1. Start with the spring torque column and select a spring end torque at 01 that equals or exceeds the maximum closing (seating) torque required for the valve.
  2. Move to the left in that spring line to a pressure column that is equal to or less than the minimum operating pressure. The pressure stroke column start (break) torque (shown at 0") must equal or exceed the maximum break torque. The pressure end torque (shown at 900) must exceed the valve torque requirement at the full open or full flow position. The pressure stroke is counterclockwise rotation.
  3. If the pressure stroke output torque value does not exceed the maximum required at each position (00 , MIN, 900) then it will be necessary to select a larger model that meets or exceeds the torque requirements in both the spring and pressure columns.
  4. Now that the actuator has been selected, use the pressure torque charts to determine that the maximum operating pressure does not exceed the maximum pressure rating of the actuator and the torque Output does not exceed the allowable torque for the valve stem at the maximum operating pressure. If either of these ratings are exceeded, the maximum operating pressure must be reduced (i.e. adding a pressure regulating valve) or an alternate actuator must be selected.
  5. At the time of order placement, it is most important to confirm/specify the direction of the spring stroke. Clockwise rotation to close is standard.

Spring Return Fail Close (CCW) Actuators

NOTE: For fail open actuators that require a counterclockwise stroke, the spring cylinder is assembled on the opposite side of the housing and the torque plug is reversed; therefore, the output torque values shown in the torque charts are unchanged but the values at the 01 and 901 positions will be reversed.

  1. Starting with the spring torque column, select a spring that has break torque (901), minimum torque (MIN) and end torque (00) values that exceed the maximum valve torque requirements.
  2. Move to the left in that spring line to a pressure column that is equal to or less than the minimum operating pressure. Verify that the minimum output torque and the output torque at the 901 position (seat torque) exceed the valve torque requirements.
  3. If the pressure stroke output torque values do not exceed the maximum valve torque requirements at each of the three positions then you must select a larger model that meets or exceeds the torque required in both the spring and pressure columns.
  4. Now that the actuator has been selected, use the pressure torque chart to determine that the maximum operating pressure does not exceed the maximum pressure rating of the actuator and the torque output does not exceed the allowable torque for the valve stem at the maximum operating pressure. If either of these ratings are exceeded, the maximum operating pressure must be reduced (i.e. adding a pressure regulating valve) or an alternate actuator must be selected.
  5. At the time of order placement, it is most important to confirm/specify the direction of the spring stroke. Clockwise rotation to close is standard.

Dimensions

Included in the SERIES M literature are outline dimensions for both double acting and spring return models. Please refer to these catalog pages to determine the physical size of the actuator selected.

NOTE: The values shown on the torque charts are minimum output based on ideal conditions. The actual torque output may vary based on adjustor stop screw position, alignment, service time between lubrication, and other influencing factors.