Direct-acting relief valve

Capacity: 50 gpm200 L/min. | Cavity: T-3A
RDFA : Direct-acting relief valve
Technical Features [ + ]

Direct-acting relief cartridges are normally closed, pressure-limiting valves used to protect hydraulic components from pressure transients. When the pressure at the inlet (port 1) reaches the valve setting, the valve starts to open to tank (port 2), throttling flow to limit the pressure rise. These valves are smooth and quiet, essentially zero leak, dirt tolerant, immune to silting and are very fast.

  • All 2-port relief cartridges (except pilot reliefs) are physically and functionally interchangeable (same flow path, same cavity for a given frame size).
  • Will accept maximum pressure at port 2; suitable for use in cross port relief circuits.
  • The seals on the adjust screw are exposed to system pressure which means this valve can only be adjusted when the pressure is removed. The setting procedure is; check the setting, remove the pressure, adjust the valve, check the new setting.
  • Valve is relatively insensitive to varying oil temperatures and oil borne contamination.
  • Select a spring range where the desired relief setting is approximately mid-range to high between the minimum and maximum pressure to ensure maximum valve repeatability.
  • Suitable for use in load holding applications.
  • Back pressure on the tank port (port 2) is directly additive to the valve setting at a 1:1 ratio.
  • Cartridges configured with EPDM seals are for use in systems with phosphate ester fluids. Exposure to petroleum based fluids, greases and lubricants will damage the seals.
  • Incorporates the Sun floating style construction to minimize the possibility of internal parts binding due to excessive installation torque and/or cavity/cartridge machining variations.
Technical Data [ + ]
Note: Data may vary by configuration. See CONFIGURATION section.
Cavity T-3A
Series 2
Capacity 50 gpm200 L/min.
Factory Pressure Settings Established at 4 gpm15 L/min.
Maximum Operating Pressure 5000 psi350 bar
Response Time - Typical 2 ms2 ms
Maximum Valve Leakage at Reseat 10 drops/min.0,7 cc/min.
Reseat >90% of setting>90% of setting
Adjustment - No. of CW Turns from Min. to Max. Setting 66
Valve Hex Size 1 1/8 in.28,6 mm
Valve Installation Torque 45 - 50 lbf ft61 - 68 Nm
Adjustment Screw Internal Hex Size 5/32 in.4 mm
Locknut Hex Size 9/16 in.15 mm
Locknut Torque 80 - 90 lbf in.9 - 10 Nm
Model Weight .50 lb0,25 kg
Seal kit - Cartridge Buna: 990303007
Seal kit - Cartridge EPDM: 990303014
Seal kit - Cartridge Polyurethane: 990303002
Seal kit - Cartridge Viton: 990303006
Performance Curves [ + ]
FAQs [ + ]

Pressure setting tolerances are listed in our Performance Data page. A link to this page can also be found in the Additional Resources tab of the applicable product page.

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

Maybe not. We build in a good amount of overlap in the kick-down reliefs to prevent false tripping. This means they are not as fast as our standard pilot-operated reliefs. A direct-acting relief valve set just above the kick-down relief valve would be good insurance.

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.

One graphic example is on a portable grain auger for silos. When the farmer gets caught in the auger the kick-down relief trips and allows him to escape.

Notes [ + ]
  • U.S. Patent #4,742,846; European Patent Pending
Additional Resources [ + ]