High-Flow, Low Cracking Pressure Flapper Check Valve, -6 Body Size

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  • High flow, low cracking pressure flapper style check valve in -6 housing size.
  • 0.04 PSI cracking pressure.
  • 300+ psi max operating backflow holding pressure, 1,000+ psi max operating pressure in normal direction of flow.
  • Exceeds most military specification requirements.
  • Made in USA.
  • Lifetime Warranty.

Lifetime Warranty

Part # FCV-06
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A Precision Check Valve that Exceeds Military Specifications


Improved Racing's patent-pending FCV-06 series check valves are an excellent choice for fuel systems and crankcase ventilation systems in turbocharged engines. These valves outperform by every measure:


  • Ultra-low flow restriction.
  • Extremely low cracking pressure.
  • Very high holding pressure.
  • Robust stainless steel and anodized aluminum construction.
  • FKM seals for compatibility with most fluids and operating temperatures up to 302°F (150°C).
  • Near-zero leak rate.

Ultra-Low Flow Restriction

Most check valve designs - including poppet check valves, ball check valves, diaphragm check valves, piston check valves, and others - are restrictive, resulting in a pressure drop across the valve even when fully open.


Improved Racing's check valves use a flapper design, originally developed for military jet engine turbines, that swings completely out of the fluid's flow path, adding virtually no flow restriction. These check valves were further optimized for low restriction at high flow rates using flow simulation software and were designed to exceed most military specification requirements.


Improved Racing's patent-pending design incorporates innovations that allow the swinging door design to be implemented in a compact valve size using small components.

FCV-06 Closed Position

High-Flow Check Valve in Open Position, Unrestricted Flow

Low Cracking Pressure

This flapper style valve has a very low cracking pressure of less than 0.04 psi, making it ideal for applications such as PCV systems. Higher cracking pressures are also possible by replacing the torsion spring.

High Holding Pressure

The valves have been tested to 1,000 psi of checked holding pressure without catastrophic failures or excessive leakage. This allows us to conservatively rate these valves to hold 300+ psi of checked pressure under normal operating conditions. For comparison, the military-grade check valves we tested failed catastrophically with complete pressure loss at less than 200 psi.

Constructed from Durable Materials

Every internal component (hinge, spring, hinge pin, and gasket core) is made from stainless steel to ensure long lasting, reliable performance and compatibility with just about any fluid, including corrosive fluids. 


The check valve's gasket is made from FKM (Viton®) rubber bonded to a stainless steel core, giving it a high operating temperature of up to 302°F (150°C). It's also highly chemical resistant and compatible with practically all fuel types.


FCV-06 High-Flow Check Valve Diagram, Closed Position

Near-Zero Leak Rate

Unlike typical valves with an all-metal construction, Improved Racing's valves provide a near-zero leak rate thanks to the FKM (Viton®) rubber seal. This means your engine will receive fuel or oil pressure immediately with no priming required.

Multiple Sizes Available

Improved Racing's check valves are available in multiple fitting sizes, and the inlet and outlet halves can be mixed and matched to create a completely custom valve in a compact space.

Features and Specifications

  • Flapper design allows for very high flow with low restriction.
  • Design optimized using flow simulation software.
  • Available with -6AN and -4AN male connections or -6AN female O-Ring boss connections.
  • FKM (Viton®) rubber seal.
  • All stainless steel internal components for compatibility with a wide range of fluids.
  • 6061-T6 billet aluminum body with black MIL-A-8625 Type II anodized finish.
  • Laser marked with flow direction and hinge location per military specification.
  • Maximum operating backflow holding pressure of 300+ psi, burst backflow holding pressure of over 1,000 psi.
  • Maximum unchecked (normal direction of flow) operating pressure of over 1,000 PSI.
  • -40°F to 302°F operating temperature range.
  • Made in USA.
  • Lifetime Warranty.


FCV-06-06AM Dimensions
-6AN Valve


FCV-06-06AM Dimensions
-4AN Valve

FCV-06-06AM Dimensions
-6AN O-Ring Boss Valve


  • Ideal for use in fuel systems, crankcase ventilation systems, oiling systems (wet sump and dry sump), coolant systems, and more.

Part #
Improved Racing
Primary Material
6061-T6 aluminum
Type II Anodized
Fitting Angle
Connection B Size
Connection B Gender
Maximum Operating Temperature
302°F (150°C)
Minimum Operating Temperature
-40°F (-40°C)
Maximum Operating Pressure
1000 psi (68.94 bar)
O-Ring / Gasket Material
FKM (Viton)
on installation only
Breather and vent lines
Fuel (in-tank)
Fuel (outside of tank)
Gauge and sensor lines
High pressure applications
High temperature applications
Hydraulics: low pressure (return lines)
Vacuum lines
Coolant & water lines
Other oil water and air systems
Fluid Compatibility
Air and gas
Engine oil
Ethanol-based fuels (E85+)
Ethanol/gasoline mixtures
Gear oil
Nitrous Oxide
Power Steering Fluid
Racing fuels
Transmission fluid
Standards & Certifications
AN Threads & 37° Flares per SAE AS4395
Milspec Type II Anodizing
O-Ring Boss Threads per SAE J1926-3 & ASME B1.1
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