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Preferred Instruments

Preferred Instruments manufactures microprocessor based controllers, instruments, and electric actuators for combustion and process applications. Preferred Instruments also manufactures oil tank gauging and leak detection equipment. A major component of the Instrument group sales is from control systems integration and personal computer based Supervisory Control and Data Acquisition systems. Preferred Utilities' industrial factory is located in Danbury, CT

Power Arm Linear Actuator

The Model PL Power Arm Actuator is a self-contained, electromechanical, linear actuator for use in remotely controlled manual or fully automatic control systems.

Power Arm Linear Actuator – Datasheet     SDI-PL Installation Manual


The “Power Arm” actuator provides a positive linear thrust for positioning dampers, louvers, jackshaft mechanisms, rotary valves, or other mechanisms.  The PL is used for 3-wire floating control in boiler draft control cases.  Though this actuator is generally used in positioning applications, it is equally suited for on/off control.


The Model PL Power Arm Actuator is a self-contained, electromechanical, linear actuator for use in remotely controlled manual or fully automatic control systems. This unit may be started, stopped or instantly reversed at any point within the stroke without damage, over heating or loss of power.  The Power Arm Actuator has a solid performance history earned by years of continuous operation in thou ands of unattended boiler room combustion installations.

Operation: In response to a SPDT control switch with a neutral position, a reversible gear motor (A) rotates an Acme threaded lead screw (B) to drive a travelling nut (C) and extend or retract the actuator ram (D). Sealed, snap action switches (E) are opened by ram mounted cams (I & J) to stop the motor and positively limit ram travel. The standard actuator includes two normally open auxiliary switches (F) that trip immediately prior to the full open or closed ram position.

Installation: Stationary or pivot mounting is available. Stationary mounting uses base (G) and stabilizing bracket (H). Attached to the ram eye (K) is a clevis that pivots as the ram extends and retracts. Pivot mounting uses only base (G). The ram eye and clevis are re placed by a length of ½” pipe threaded into the ram end.  As the ram ex tends and re tracts, the actuator is free to pivot on the base. Pivot mounting permits the use of straight line, push-pull link age that reduces ram friction with result ant pro longed ram and bearing life.


  • Adjustable 1″ – 6″ Travel Electric Actuator
  • 200 lbs Output Thrust
  • Designed For Modulation Service
  • Self-Locking Drive System To Hold In Last Position
  • Two Infinitely Adjustable Auxiliary Limit Switches
  • Isolated Position Feedback Available With R-AL and R-ALP Models
  • Integral 4-20 mADC Positioner Circuit Board Available With R-ALP Models

Power: 120 VAC, 50/60 Hz, 60 VA

Ambient Temperature: 150° F (65° C) Maximum

Input: Switching SPDT or Floating Contacts, or 4-20 mADC, 0-5VDC, 0-1000 Ohms or 0-135 Ohms

Load: 100 lbs. or 200 lbs. Thrust

Stroke: 1″ – 6″ Adjustable

Speed: 6″ in 30 or 60 Seconds

Auxiliary Switches: Two Integral, Enclosed, 15A, ⅛ HP @ 120 VAC

Position Feedback: Precision Potentiometer, 1000 Ohm

Manual Operation: Hand Wheel (Optional)

Linkage: Ram Eye, Catalog Number 20040 Included; Connecting Linkage Optional

Motor: Sealed, Permanently Lubricated, Continuous Duty, Capacity Start and Run, 3 Wire Reversible

Dimensions: 6 ⅞” H x 11 ⅞” L x 8 ¾” D

Enclosure: 14 Gauge Stainless Steel, Fully Gasketed

Installation: Stationary or Pivot Mounting


The actuator shall be totally enclosed, have a six inch stroke and 200 lbs of push or pull thrust. The drive mechanism shall include a permanently lubricated, continuous duty rated, ball bearing type gear motor to drive an Acme threaded lead screw, travelling nut and thrust ram. The actuator shall be installed so as to pivot on its base as the ram extends and retracts. Linkage shall include an adjustable drive rod and cast iron crank arm. The actuator shall be Preferred Instruments, Danbury, CT, Model PL.