Why Hydraulic Pump Intake Isolation Valves Are Not Compulsory

500HPU3One of our members wrote me with this question:

“I’d like to hear your opinion about isolation valves on pump intake lines. Within our company there is an ongoing debate over whether we should use a more expensive ball valve or a cheaper butterfly valve?”

At the root of this question is the negative effect of turbulence in the pump intake line. The argument for using a ball valve as an intake line isolation valve is, when it’s open, the full bore of the valve is available for oil flow. So if you have a 2″ ball valve in a 2″ intake line, when the valve is open, from the oil’s point of view at least, it’s as if it wasn’t there at all.… continue reading »

One Thing You Must Check Before Switching Hydraulic Oils

hydraulic oil drumThe issues which can arise when switching brand and/or type of hydraulic oil, is a question I get a lot. And the crux of this problem, is:
1. You can never completely drain ALL of the original oil out of the hydraulic system; and therefore:
2. There WILL be some mixing of the original and the new oil, so how do you make sure they are miscible (compatible)?

Oil additive makers and oil blenders face the very same issue when they want to run field trials to compare the performance of their latest creation with an existing ‘control’ fluid. And the way these guys approach this problem offers some insight for us regular hydraulic hacks.… continue reading »

Why Hydraulic Motor Drain Lines Are Compulsory Even When They’re Optional

gear motor without external drainAs you’re hopefully well aware, an unrestricted case-drain line is essential on a piston-type hydraulic motor, whether it’s axial, radial or bent-axis design. But when it comes to gear designs: external, internal and gerotor, a case-drain line is generally considered optional. This is because these types of motors don’t have a large-volume case or sump like piston motors do. But they do have internal leakage which by design, usually accumulates in a small cavity just before the shaft seal.

In theory, by installing a high-pressure shaft seal and two check valves as shown in the inset picture, internal leakage is drained into the return line (something that’s not acceptable for a piston motor or pump).… continue reading »