A hydraulic machine has lots of moving parts to maintain. In fact, a hydraulic system is one of the most complex systems to maintain effectively. And here’s one more item to add to the list: the machine’s drawings. A machine’s hydraulic (and electrical) schematic diagrams don’t wear out, but they do tend to become inaccurate over time.

Even absent a major refit or redesign, it is not unusual for minor changes to be made to the hydraulic circuit over the course of the machine’s life. This could involve: change in make or model of components; additional filtration–or a reduction in filtration components, if, for example, a suction strainer is removed; re-routing of conductors–drain lines for example; installation of additional cooling capacity or the installation of pressure test points, oil sample points and other maintenance accessories.… continue reading »

Air is both a normal ingredient, and a contaminant, of hydraulic oil. It’s a normal ingredient because hydraulic fluid typically contains between 6 and 12 percent by volume of dissolved air. There’s no avoiding this. And provided this dissolved air stays dissolved, it poses no problem to the hydraulic system or the fluid.

But if this dissolved air comes out of solution, or air is ingressed via the pump intake for example, the result is entrained air: air bubbles typically less than 1-millimeter in diameter dispersed throughout the fluid.

Entrained air increases noise levels and decreases the efficiency of the system by reducing bulk modulus (fluid stiffness).… continue reading »

During a recent conversation with a client, the issue of testing hydraulic pump rebuilds came up. As I explain in Insider Secrets to Hydraulics, it is essential that all hydraulic components are properly tested after rebuild. Ensuring a repaired component will perform the way it should when it’s installed on the machine BEFORE it leaves the repair shop, instills confidence in the customer and the repairer. And this is especially important for hydraulic pumps.

But this conversation was about testing BIG pumps. For example, Rexroth A7VSL1000 and A4VSO1000 (1000 cc/rev). Any purchasing officer who has been around a while understands that if she issues a purchase order for a pump rebuild, the expectation is the rebuilt pump should come with a test certificate, which ideally shows the pump has been tested to full flow and pressure prior to dispatch.… continue reading »