The 156 Lee Chek high-pressure check valve from The Lee Co., Westbrook, Conn. (theleeco.com), weighs only 0.7 gm, and has a 0.156-in. diameter.
This gives the valve an installed envelope less than half the size of a 0.187-in.-diameter high-pressure check valve. The all-steel valves are available in forward-flow configurations with working pressure to 5,000 psid. Cracking pressure is either 5 ±3 or 1 ±0.5 (psid), depending on the model. And the Lohm rate is 250. (A Lohm is the company's measure of resistance to fluid flow. By definition, 1 Lohm will flow 100 gpm with a pressure drop of 25 psi at 80°F. Therefore, Lohms for a system equal 100 divided by the flow in gpm @25 psid.)