I'm developing a test to look at the stress-strain characteristics of polyurethane foams under hydrostatic loading. The test requires a constant strain rate (e.g. constant flow rate into the test chamber) and readings of chamber pressure (stress) and the amount of fluid pumped into the chamber (strain) as a function of time. I can measure the pressure, but have not figured out a good way to control the flow rate or measure it. We need a scheme to set up a constant flow rate into th pressure vessel where the amount of fluid is small (8 in^3) but the rate is high (up to 40 gal/sec) and the duration is short (0.07 sec). Accuracy on the integrated volume measurement needs to be better than 3 cm^3. We can use water or hydraulic oil (water preferred) and have to reach chamber pressures near 2000 psi. Any ideas?