Ventable, pilot operated, balanced piston relief main stage with integral T-8A control cavity - before check

Capacity: 10 gpm40 L/min. | Cavity: T-21A
HVCA8 : Ventable, pilot operated, balanced piston relief main stage with integral T-8A control cavity - before check
Technical Features [ + ]

The relief-before-check cartridge is a CavitySaver™ (multi-function) valve incorporating a normally closed, balanced piston modulating element tee'd in before a check function. The valve incorporates an integral pilot control cavity. The pilot control cavity will accept any T-8A pressure control cartridge. When the pressure at the inlet (port 2) reaches the pilot control valve setting, the modulating element starts to open to tank (port 3), throttling flow to regulate the pressure. The T-8A pilot section is drained to port 4. The check valve flow is from the inlet (port 2) to the system port (port1).

  • Note! This valve deviates from Sun's normal flow path for relief valves. It is probably not useable in current Sun relief manifolds.
  • 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.
  • The main stage orifice is protected against contamination.
  • The check portion of the valve has a maximum leakage rate of less than 1 drop/minute (0,07 cc/min).
  • One purpose of this dual function cartridge is to offer pump isolation and relief protection in single and/or multiple pump circuits. Another purpose is to act as a main stage in an accumulator sense, pump unload circuit.
  • NOTE: With the -8 control option, the main stage valve should first be installed to the correct torque value. The T-8A pilot control valve should then be installed into the main stage valve to its required torque value.
  • The -8 control option allows the pilot control valve to be incorporated directly into the end of the relief cartridge via the T-8A cavity. These pilot control cartridges are sold separately and include electro-proportional, solenoid, air pilot, and hydraulic pilot operation. See Pilot Control Cartridges.
  • 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-21A
Series 1
Capacity 10 gpm40 L/min.
Factory Pressure Settings Established at 4 gpm15 L/min.
Maximum Operating Pressure 5000 psi350 bar
Response Time - Typical 10 ms10 ms
Maximum Valve Leakage at 110 SUS (24 cSt) 2 in³/min.@1000 psi30 cc/min.@70 bar
Check Cracking Pressure 25 psi1,7 bar
Pilot Control Cavity T-8AT-8A
Pilot Control Valve Installation Torque 20 - 25 lbf ft27 - 33 Nm
Valve Hex Size 7/8 in.22,2 mm
Valve Installation Torque 30 - 35 lbf ft41 - 47 Nm
Seal kit - Cartridge Buna: 990021007
Seal kit - Cartridge EPDM: 990021014
Seal kit - Cartridge Polyurethane: 990021002
Seal kit - Cartridge Viton: 990021006
Performance Curves [ + ]
FAQs [ + ]

The kick-down relief acts much like a circuit breaker. When the pressure at the inlet (port 1) of the relief valve rises to the setting, the valve pops open and drops the pressure down to 100 psi or so. The valve stays open until flow through it stops. Shutting off the supply of oil will reset the valve; reversing pressure on the valve is a positive way of resetting it.

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.

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

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.

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.

Notes [ + ]
  • Compound cartridge (pilot and main stage) assembly information is provided for reference only. Cartridges must be ordered separately and assembled at point of use.
Additional Resources [ + ]