RPKS8 | Cartridges » Pressure Control » Relief

This valve is a normally closed modulating element that incorporates an integral pilot control cavity. It is a balanced poppet design. The pilot control cavity will accept any T-8A pressure control cartridge. When the pressure at the inlet (port 1) reaches the pilot control cartridge's setting, the poppet element starts to open to tank (port 2), throttling flow to regulate the pressure. The pilot cartridge's setting determines the difference in pressure between port 1 and port 2.

Because the modulating occurs inside the cartridge, these valves are immune to most of the problems associated with cavitation, namely noise and manifold erosion.
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.
Valve is relatively insensitive to varying oil temperatures and oil borne contamination.
Main stage orifice is protected by a 150-micron stainless steel screen.
Back pressure on the tank port (port 2) is directly additive to the valve setting at a 1:1 ratio.
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.

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Note: Data may vary by configuration. See CONFIGURATION section.

Cavity	T-18A
Series	4
Capacity	200 gpm760 L/min.
Maximum Operating Pressure	5000 psi350 bar
Factory Pressure Settings Established at	4 gpm15 L/min.
Control Pilot Flow	15 - 20 in³/min.0,25 - 0,33 L/min.
Pilot Control Cavity	T-8AT-8A
Pilot Control Valve Installation Torque	20 - 25 lbf ft27 - 33 Nm
Pilot Control Valve Hex Size	7/8 in.22,2 mm
Main stage leakage at reseat	10 drops/min.0,7 cc/min.
Response Time - Typical	2 ms2 ms
Valve Hex Size	1 5/8 in.41,3 mm
Valve Installation Torque	350 - 375 lbf ft474 - 508 Nm
Model Weight	2.50 lb1,15 kg
Seal kit - Cartridge	Buna: 990318007
Seal kit - Cartridge	Polyurethane: 990018002
Seal kit - Cartridge	Viton: 990318006

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Performance Curve for RPKS8: Pilot-operated, balanced poppet relief main stage with integral T-8A control cavity

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Direct acting or pilot operated - what do I use?

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.

How do I get a kick-down relief to reset?

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.

Where would I use a kick-down relief?

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.

How big is a drop of hydraulic oil?

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

What are the tolerances on pressure settings for Sun's pressure control valves?

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.

Can I use a kick-down relief for my system relief?

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.

What parts of the Sun cartridge valve are field serviceable?

Only external seals are serviceable. Sun offers replacement seal kits for all cartridge models. The applicable kit part number can be found in the product page's Technical Data table or by using our Cartridge Seal Kit search function located under Accessories. Please note: Converting the external seals from one material to another does not ensure fluid compatibility with that material due to the existence of internal seals within the cartridge.

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RPKSPilot-operated, balanced poppet relief valve

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Compound cartridge (pilot and main stage) assembly information is provided for reference only. Cartridges must be ordered separately and assembled at point of use.

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Highlights