Denison Problem Solving

Denison Hydrostatic Parts and Repair

We service Denison hydrostatic pumps

Hydrostatic Transmission Service, LLC Offers Denison Hydrostatic Parts and Denison Hydrostatic Repair.

We want our customers to know our process! Give us a call at 800-361-0028 or Email us at

Problem Solving

Effect of Trouble Probable Cause Some of the Remedies for theProblem
High wear in pump Unwanted water in fluid Water vapor Faulty breather, strainer Heat exchanger leakage ' wrongful clean-up practice Water in makeup fluid
Pressure shocks Cogging load Worn release valve Mechanical considerations Needed repairs
Pressure shocks Worn compensator Slow response in check valves Make repairs Replace or relocate
Pressure shocks Servo pressure too low to sustain firm control Increase pressure and check pressure drop through servo filter
Pressure shocks Too much decompression energy rates Improve decompression control
Pressure shocks Excessive line capacitance (line volume, line stretch, accumulator effects) Lower line size or lengths. Get rid of hose Bleed air
Pressure shocks Barrel blow-off Double check pump hold-down, rotary motion group, drain pressure
Heating of fluid Excessive pump leakage Look over again the case drain flow and repair as required Fluid too thin Improper assembly, port timing
Heating of fluid Relief valve Set too low (compared to load or to compensator) Not stable enough that is caused by back pressure, worn parts
Heating of fluid Compensator Set too high (compared to release) Worn parts
Heating of fluid Pump too large for fluid needs Choose smaller pump displacement
Heating of fluid Heat exchanger Water turned off or too little flow Water too hot Fan clogged or restricted Efficiency lowered by mud or scale deposits On and off hydraulic fluid flow
Heating of fluid Reservoir Too little fluid Entrained air in fluid Improper baffles Keeping in air blanket that prevents heat rejection Heat pickup from adjacent equipment

Revised Limits of Wear Parts

11 and 14 in.3 Original Dimension Max. Revised From Original Dimension Min. Dimension After Revised
Port plate face .725/.715" .010" .705"
Cylinder barrel face 5.880" .010" 5.870"
Shoe retainer face .4387.437" .005" .432"
Piston shoe face (pocket) .020" .010" .010"
Creep plate face .251/.250" .010" .240"
Face plate None Replace

Part problems and circuit problems are frequently inter-related. A faulty circuit may work with obvious success but will cause failure of a particular part within it. The part failure is effect, not the reason of the problem. This broad guide is on hand to help in locating and eliminating the cause of problems by studying their effects.

Problem Solving

Effect of Trouble Probable Cause Some of the Remedies for theProblem
Noisy Pump Air in Fluid Leak in suction line Leak at shaft seal Low fluid level Turbulent fluid Return lines above fluid level Gas leak from accumulator Too much pressure drop in the inlet line from a pressurized reservoir Suction line strainer trying to be an air trap as well
Noisy Pump Cavitations in pump or motor rotating group Fluid too cold and viscous Fluid too heavy Shaft speed too high Suction line too small Suction line collapsed Suction strainer too small Suction strainer not clean Working altitude too high Boost or replenishment pressure too low Replenishment flow too small for dynamic conditions
Noisy Pump Misaligned shaft Faulty installation Improper in mounting Axial interference Faulty coupling Extreme overhung loads
Noisy Pump Mechanical fault in pump Piston and shoe looseness or failure Bearing failure Incorrect port plate selection or index Eroded or worn parts in the displacement control
Erosion on barrel ports and port plate Air in fluid See above
Erosion on barrel ports and port plate Cavitations See above
High wear in pump Excessive loads Lower pressure settings Reduce speeds
High wear in pump Contaminant particles in fluid Faulty filter maintenance Filters too coarse Putting in dirty fluid to system Reservoir openings Reservoir breather Improper line replacement
High wear in pump Improper fluid Fluid too thin or thick for working temperature range Breakdown of fluid with time/temperature/shearing effects wrong additives in new fluid Breakdown of additive effectiveness with chemical aging
High wear in pump Improper repair Incorrect parts,procedures, dimensions, finishes

Denison Repair and Parts List

  • Establish straight thread connectors (3) and O- rings (4) into threaded holes in cradle.
  • Fit in right and left hand pressure feed tubes (5 and 6) to connectors (3). Tighten connectors till it is snug.
  • Place the mounting flange (9) with the large open end facing up and Put together two dowel pins (8) in the cradle mounting area and four locating sleeves (10) in the outer edge of the flange.
  • Mount the rocker cam and cradle assembly (7) over the dowel pins (8) in the mounting flange.
  • With cam and cradle put in, place mounting flange on the side and install two 3/8-16 x 2 screws through the seal retainer surface into the cradle. These screws do hold in the rocker cam assembly in place and will be taken out later.
  • Bring back the mounting flange to an straight up an down position and slant the rocker cam to both extremes of attitudes in the cradle.
  • Situate the barrel and auxiliary shaft assembly (1) directly over the pistons. Beginning with the uppermost piston, steer them one at a time into the barrel bores. Going back to the cam to a level position in the cradle.

Continued Denison Repair

  • Put in the faceplate pins (1) in the holes given in the barrel face.
  • Apply lubrication to the surface of the barrel and place l the faceplate (2) over the faceplate pins. Warning Make certain the faceplate is correctly seated on the barrel and pins with the steel side towards the barrel face. The faceplate has one side bronzed and this should be toward the port plate. If needed, remove coating from edge of plate to settle on bronze side.
  • Put in gaskets (3) over the two dowel pins in the mounting flange.
  • Put together the housing assembly (4) over the bar rel and auxiliary shaft assembly. Cautiously guide the override tubes and pressure feed tubes (items 2, 5 and 6, Figure 4) into the housing assembly. Place the pressure feed tubes in the slots in the housing face

Problem Solving

No. Qty. Pirt No. Explanation
1 1 See Fig 3 Barrel & auxiliary shaft ass y
2 2 033-71609 Override pressure lubes
3 2 492-15265 Connector
4 2 691-00902 0-ring
5 1 S1 3-43967 Tubing ass y (right side)
6 1 S1 3-43966 Tubing ass y (left side)
7 1 See Fig. 2 Rocker cam & stroking ass y
8 2 324-23216 Dowel pin
9 1 033-71546 Mounting flange
10 4 033-72664 Locating sleeve

Problem Solving

No. Qty. Pirt No. Description
1 2 033-49825 Face plate pins
1 2 033-71921 Barrel face plate P1 1 P only
2 1 033-71575 Barrel (ace plate P1 4P only
3 1 033-71602 Housing gasket
4 1 See Fig. 5 Housing assembly
Guidelines for Replenishing Circuit Isolation Plug

The isolation plug together with this is to be used only if an external filter circuit is not offered DO NOT operate this unit with the isolation plug put in unless an outside line has been provided. When the outer filter circuit is not used, dispose of the isolation plug. When the outside filter circuit is used, fit the isolation plug under the plug in the face of the port block. Use a 3/16" hex wrench, 4" minimum in length. Insert the isolation plug and tighten to 80-120 in./lbs. torque. Warning Filter should have a bypass and bypass indicator and Hydrostatic Transmission Service,LLC which offers Denison recommends that it be sized four times for projected flow.

For a list of our Eaton pumps and prices, go to our  Eaton hydrostatic parts page

Visit us at our  EBay store: Hydrostatic Transmission Service, LLC



We accept almost all forms of payment. If you have a payment question, give us a call.


404 Air Park Road, Tupelo, MS 38801


(800) 361-0068