High-Flow, Low Cracking Pressure Flapper Check Valve, -12 Body Size

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  • High flow, low cracking pressure flapper style check valve in -12 Body Size
  • Exceeds most military specification requirements
  • Made in USA, Lifetime Warranty

Lifetime Warranty

Part # FCV-12

Improved Racing set out to design the highest flowing check valve we could and this is the result!

Low Restriction to Flow

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.

High Holding Pressure

The valves have been tested at up to 1,000 psi of backflow holding pressure without catastrophic failures or excessive leakage. This allows us to very safely rate these valves to hold 300 psi of backflow pressure under normal operating conditions with a very high factor of safety. For comparison, the military surplus flapper check valves we tested failed catastrophically with complete pressure loss at less than 200 psi.

Low Cracking Pressure

This flapper style valve has a very low cracking pressure of less than 0.05 psi. 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. It's also highly chemical resistant and compatible with all types of fuel.

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 using our custom check valve configurator.

FCV-12 High-Flow Check Valve Diagram, Closed Position


FCV-12 Closed Position

High-Flow Check Valve in Open Position, Unrestricted Flow

Features and Specifications

  • Flapper design allows for very high flow with low restriction
  • Design optimized using flow simulation software
  • 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


Below are the overall dimensions for some common valve configurations:

FCV-12 -8AN Check Valve Dimensions

-8AN Male

FCV-12 -10AN Check Valve Dimensions

-10AN Male

FCV-12 -10AN ORB Check Valve Dimensions

-10AN O-Ring Boss Female

FCV-12 -12AN Male Check Valve Dimensions

-12AN Male



  • Ideal for use in oiling systems (wet sump and dry sump), fuel systems, crankcase pressure ventilation 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
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
Instruction Manuals
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