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Case Drain and Fill Operation



The purpose for attaching the case drain from the hydraulic drive motor to the inlet of the oil heat pump is to eliminate the need for periodic oil changes in the oil heat systems with the small Kenway expansion tank. Some customers were experiencing oil breakdown in their oil heat systems due to high temperatures created in a small amount of oil (1 – 2 quarts). Regular oil changes are necessary to insure the oil stays in good condition.


This design replaces the earlier system that required 1 – 2 quarts of Dexron transmission fluid. It allows the oil from the Kenway motor assembly case drain to enter the inlet of the oil heat pump. The additional oil will overflow the oil heat system and will exit the expansion tank. Mixing of the oils will occur and filtering of the oil will take place in the main hydraulic system reservoir.

The case drain line leaving the overflow tank should be routed to the main tank return line. Do not route with other case drain lines if possible. Back pressure on the case drain lines need to be kept to a minimum – under 25 psi under any operating condition to protect the front pump seal from being pushed out of its seat.


Filling the oil heat system with oil after all heater lines, case drain lines, and motor inlet and outlet lines have been connected is done by the motor case drain.

  1. Set the heater controls to the ‘off’ position.
  2. Place a pressure gauge in the line between the motor and the pump to check case drain back-pressure.
    Start the machine and check for leaks and that the hydraulic motor is turning clockwise - as viewed from the pulley end of the motor.
  3. Let the machine idle for a few minutes and check for flow through the case drain line.
  4. Once there is oil flowing through the case drain, set the heater temperature control to ‘off’ and set the master toggle switch to ‘heat’. Set the toggle switch on the hydraulic drive to ‘on’.
  5. Let the oil heat pump circulate for a few minutes to work the air out of the oil heat system.
  6. When satisfied that all the air is out of the system, set the heater temperature control to ‘maximum heat’.
    This will change the sound of the oil heat system and heating should begin almost immediately.
  7. If the pressure in the case drain line exceeds 25 psi or no oil is entering the system check the flow of oil from motor – it should be from .25 - 1 gpm. If there is too little or excessive case drain leakage, replace the motor. If there is proper case drain flow, check the case drain hose or the main tank return line and correct any problems. Retest the case drain pressure.
  8. Remove the pressure gauge (if installed) from the case drain line. Check for leaks one more time.
  9. No other servicing of the oil is required. The oil from the main reservoir is filtered. Normal maintenance of the oil is all that is required.