Pressure Independence Module Page - 2

How It Operates

The built in transducer is connected with 1/4" tubing to a static pressure fitting located in the duct at the point of control. This transducer is a mass air flow sensor which measures the air flow (0.007 cfm max.) from the duct to a port open to atmosphere and converts that to a voltage output indicating differential pressure. For differential pressure above set point, discharge and zone dampers are rotated closed and bypass dampers rotated open. The opposite happens when the differential pressure is below set point. Dual motors provide the rotation - one operating clockwise and the other counterclockwise.

Installation

Pre Installation Check

Check to make sure this PIM is connected correctly for the application. If not, swap the top and bottom motor leads. (Show change on the inside of the PIM cover by erasing the existing X and X'ing the other block.)

• Discharge / Zone damper
  Normally open with low pressure or fan off, damper closes with rising pressure. Top motor connected to terminals 11 & 12. Bottom motor connected to terminals 13 & 14.
• Bypass damper
  Normally closed with low pressure or fan off, damper opens with rising pressure. Top motor connected to terminals 13 & 14. Bottom motor connected to terminals 11 & 12.

Installation Procedure

1. Install damper in duct. Do not interfere with operation of damper blades - watch length of screws and insulation. If PIM is supplied loose from damper.
   a.) Connect to damper shaft (1/2" dia. nominal) by placing over shaft and tightening two allen screws on the actuator hub, and
   b.) Anchor PIM from turning by attaching a bracket between the damper and the bottom of the PIM.
2. Install the static pressure fitting (shipped inside the PIM enclosure.) Locate the static pressure fitting in the duct 1/2 to 2/3 of the distance between the first and the last takeoff and after at least 6 diameters of straight run. Drill a 3/8" hole in the duct, insert fitting and fasten in place.
3. Remove any rubber protection plugs from transducer and filter ports.
4. Run 1/4" pneumatic tubing (supplied by others)  from the static pressure fitting to the filter on the bottom of the PIM enclosure. (The upper transducer port, P2, is open to atmosphere.)
5. Connect electric power.
   a.) 120v/1Ø/50-60 Hz units are supplied with a transformer. Use wire nuts to connect 120v to the black and white transformer primary leads.
   b.) 24v/1Ø/50-60 Hz units do not have a transformer. Connect 24v leads to terminals 9 & 10.

Power Check

The power to the PIM is correct if the voltage across terminals 4 & 5 is 9.1v D.C.

Balancing

VAV systems are balanced for design cfm at maximum air flow. For maximum air flow to the system, PIM's installed as discharge/zone dampers should be open and PIM's installed as bypass dampers should be closed. Remove the pneumatic tubing from the filter and discharge/zone dampers should open band bypass dampers should close. If this does not happen check:

1. Top and bottom motors connected correctly (see Pre Installation Check.)
2. Static pressure set point, see below.

While balancing use magnahelic or other pressure gauge to record the static pressure from the static pressure fitting when the system is operating at design cfm. This is the static pressure that should be used as the PIM static pressure set point in this system.

Upon completion of balancing, reconnect the pneumatic tubing between the filter and the static pressure fitting.

Adjusting Static Pressure Set Point

Determine static pressure set point wanted. Preferably use the static pressure measured at the static pressure fitting during balancing with the system operating at design cfm. Otherwise begin with a .2" wg setting (1.55v.)

Measure the voltage across terminals 4 & 6 and adjust the slotted screw on the relay module to obtain the voltage corresponding to the wanted static pressure in the following table.

Control Module Dimensions

Damper Dimensions

Damper sizes are specified width (first) by height. Sizes begin at 6 x 6 and increase in 2 inch increments to 48(W) x 36(H).

Specification

Static pressure control stations shall be Pressure Independence Modules (PIM) manufactured by Acutherm, Hayward, CA.

They shall consist of a control module mounted on a damper tested to AMCA standards.

Control modules shall be field adjustable for static pressures from .05" wg to .50" wg. The control module shall consist of actuator, controls an pressure transducer fully assembled and packaged for easy installation by connecting the tubing from the static pressure fitting and the input voltage.

Voltage shall be either 24v/1Ø/50-60 Hz or 120v/1Ø/50-60 Hz. An energy limiting transformer rated at 20VA shall be factory installed in all 120v. Control modules. Maximum current draw shall be 15VA.

The actuator shall be dual synchronous motors which can turn the damper shaft clockwise or counterclockwise with a gear design capable of withstanding a stall condition at either end of the damper rotation with no detrimental temperature rise. The actuator shall mount directly on a 1/2" diameter damper shaft.

The controls shall be electronic solid state and fully contained with the control module. Field adjustment of static pressure set point shall be by turning a slotted head adjusting screw. A scale shall be located around the adjusting screw for a rough static pressure setting and an exact static pressure setting shall be made by correlating voltage readings with tabulated static pressure.

Pressure transducer shall measure pressure differential between atmosphere and the tubing from the static pressure fitting. A 5 micron filter shall be factory installed in the line from the static pressure probe to protect the transducer from contaminants.

The control module shall be field converted from direct acting to bypass by swapping the electrical leads from the dual motors.

Control module shall be in a NEMA 1 enclosure. All 120v components shall be UL rated.

A static pressure fitting shall be included for mounting in the downstream duct. Tubing between static fitting and control module is by others.

Manufacturer shall provide a 2 year warranty.