"I have a two section vane pump with new cartridges.
The problem is, one cartridge has no oil coming out when we crack open the hydraulic line going to the control valve. When we tigthen the fitting the hose reacts as if it has pressure in it.
When we crack it again - nothing."
Assuming the cartridge is the correct rotation, then this is most likely a priming issue.
You see, unlike most other hydraulic pumps, vane pumps can be finicky darn things to get pumping.
This is because - unlike a vane motor, the vanes in a vane pump don't have springs to hold the vanes in contact with the cam ring.
Centrifugal force is SUPPOSED to throw the vanes out against the cam-ring. But based on my experience, it doesn't always work out that way.
A downstream resistance is sometimes necessary to create back-pressure to hydraulically acutate the vanes against the cam ring, so the pump primes.
The solution is usually simple enough. Ensure there's a head of oil above the outlet port. If the valve bank is below the pump, then head can be achieved by routing the hose so that at some point, it extends a foot or so higher than the outlet port.

By Brendan Casey