The BIG Damaging Effects of Small Air Bubbles

cavitation erosion on valve plateAir 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 … continue reading »

The Truth About Hydraulic Pump Testing

Rexroth A2VSL1000 hydraulic pumpDuring 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 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 … continue reading »

What Causes ‘Soft’ Hard Chrome?

cyl-rod-scratchesI was recently consulted about a situation where the glass-reinforced nylon, rod guide-bush in a hydraulic cylinder was scratching the hard chrome plated rod. So in effect, the guide-bush was harder than the hard chrome plating. And this should NOT be the case. In other words the hard chrome plating on the rod was soft. Or more correctly, not hard enough. The hardness of the chrome plating should be Rockwell C (Rc) 65 minimum, and preferably higher.

So how can the hard chrome plating end up not being hard enough? This can happen when the surface area of the cylinder … continue reading »