Hydrostatic transmission flushing assembly with cross-port relief


Function for XRGN
Port Designators [ + ]
Modifiers Ports
5, 5/S Ports 1 & 2: 1 1/4" Code 62; Port T: SAE 12; Gage Ports: SAE 6; Mounting Holes: .375 - 16UNC x .75 DP;
5/M, 5/T Ports 1 & 2: 1 1/4" Code 62; Port T: 3/4" BSPP; Gage Ports: 1/4" BSPP; Mounting Holes: M10 x 1.5-6H x .75 DP;
Technical Features [ + ]

This valve assembly provides high pressure cross-port relief protection and a flushing circuit for hydrostatic transmissions. The hot oil flushing circuit allows a discharge of oil from the low pressure side of the loop. The charge pump replaces the hot, dirty oil with cool, filtered oil. The hot oil discharge is often passed through the cases of the pump and the motor, flushing hot, dirty oil from them as well.

  • A unique feature of the hot oil shuttle is that the setting of the hot oil relief can be confirmed or adjusted when the transmission is in neutral.
  • The two ports marked 1 are common as are the two marked 2. Therefore the assembly can be teed off the loop rather than being plumbed into the loop.
  • The two ports marked 1 are common as are the two marked 2. The high pressure relief that is physically on the same side as port 1 controls the pressure on port 2 and vice versa.
  • When the transmission is in neutral the charge pressure is controlled by the charge pump relief. When the hot oil shuttle opens, some or all of the charge pump flow is redirected to the hot oil relief. The charge pump relief must be set higher than the hot oil relief to produce hot oil flow. The higher the differential pressure between the 2 reliefs, the higher the hot oil flow. The amount of hot oil flow is determined by the pressure vrs flow curves of the 2 reliefs and is difficult to quantify.
  • The standard setting of the hot oil relief is 200 psi (14 bar) at a flow of 4 gpm (16 L/min).
  • Hydraulic motors leak. Therefore a mechanical brake is recommended to positively lock any stopped live load.
Technical Data [ + ]
Body Type Line mountLine mount
Capacity 40 gpm160 L/min.
Mounting Hole Quantity 44
FAQs [ + ]

There are exactly 250 Sun drops in a cubic inch or 15 in a cc.

Reasons to anodize:

  • To increase corrosion resistance. Sun uses 6061-T651 aluminum. It is one of the most corrosion resistant aluminum alloys there is. Whether or not anodizing improves the corrosion resistance of 6061 aluminum is debatable. We have yet to have a manifold returned because of corrosion.
  • Appearance (color). The 2 colors that would appeal to Sun would be blue or black. Unfortunately these are the colors that are hardest to do consistently.
  • To provide a hard wear surface. Sun does not make parts-in-body valves. The manifold is just plumbing. We don't need a wear surface.
  • Because everyone else does it. Bad reason. 

Reasons to not anodize:

  • Cost. It's another process.
  • Logistics. When you make tens of thousands of manifolds a month and you anodize hundreds, it's a problem. Consistency. See above.
  • Stamping. After a body is anodized you cannot do any more stamping without making a mess.
    Inspection. Have you ever tried to look for burrs in a black anodized body? It's the old blackboard factory at night scenario.
  • Torque. You will experience an increase in breakaway torque when removing items from an anodized manifold.
  • Fatigue life. This is the best reason to not anodize. Fatigue failure is a very complex phenomenon. What it takes to initiate a crack is difficult to predict. What it takes to propagate a crack is readily defined. Anodizing produces a very thin, very hard, and very brittle surface on aluminum. The first time you pressurize an anodized aluminum manifold you have initiated fatigue cracks. Whether or not the stress is enough to propagate the cracks is a matter of pressure and manifold geometry. Anodizing an aluminum manifold grossly reduces the fatigue life by anywhere from 20% to 50%.

Direct-acting valves are used to prevent over pressure, and pilot-operated valves are used to regulate pressure. If you are unsure, use a direct-acting valve. Sun's direct acting valves are very fast, dirt tolerant, stable, and robust. Sun's pilot-operated valves are moderately fast, they have a low pressure rise vs. flow curve, and they are easy to adjust.

Notes [ + ]
  • A mechanical brake is recommended to positively lock any stopped live load.
  • Important: Carefully consider the maximum system pressure. The pressure rating of the manifold is dependent on the manifold material, with the port type/size a secondary consideration. Manifolds constructed of aluminum are not rated for pressures higher than 3000 psi (210 bar), regardless of the port type/size specified.
  • For detailed information regarding the cartridges contained in this assembly, click on the models codes shown in the Included Components tab.
Additional Resources [ + ]