Hydrostatic transmission assembly, with cross-port relief


Function for YRGU
Port Designators [ + ]
Modifiers Ports
C, C/S Ports 1 & 2: 1/2" NPTF; Port T: 3/8" NPTF;
D, D/S Ports 1 & 2: 3/4" NPTF; Port T: 3/8" NPTF;
K, K/S Ports 1 & 2: SAE 10; Port T: SAE 8;
L, L/S Ports 1 & 2: SAE 12; Port T: SAE 8;
V, V/S Ports 1 & 2: 1/2" BSPP; Port T: 3/8" BSPP;
W, W/S Ports 1 & 2: 3/4" BSPP; Port T: 3/8" BSPP;
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.
  • 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 Motor mountMotor mount
Interface Eaton/Char-Lynn 2000Eaton/Char-Lynn 2000
Capacity 10 gpm40 L/min.
FAQs [ + ]

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

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 [ + ]
  • 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.
Additional Resources [ + ]