In chapter 13 of The Hydraulic Maintenance Handbook, I discuss the principle of engineering out issues that have the potential to cause recurring maintenance problems. Since maintenance occurs after the event, that is, after the machine is designed and built, this strategy is very much a retrospective one. Which means it’s desirable and preferable not to engineer in such potential problems in the first place.
And I was reminded of this recently. While conducting failure analysis for a client, small flakes of paint were found to be present on and in parts of the failed piston pump’s rotating group. … continue reading »
One of the key advantages of direct-acting relief valves, in comparison to their pilot-operated cousins, is fast response. And their fast response makes direct-acting reliefs the valve of choice in situations where pressure spikes are possible and must be minimized. Secondary relief valves in an actuator circuit and the ‘spike relief’ for a variable-displacement pump are common examples.
But as a general rule, direct-acting relief valves suffer more from pressure override than their pilot-operated counterparts. Pressure override is the difference between the valve’s full flow pressure and its cracking pressure.
For example: if a relief valve is set so that … continue reading »
If you know something about load sensing systems, the above headline, ‘inefficient load sensing’ appears to be a contradiction. After all, load sensing circuits match pump flow to actuator demand. And this is supposed to increase the hydraulic system’s efficiency. Not reduce it.
HOWEVER, under certain conditions a load sensing hydraulic system can be VERY inefficient. Let me give you a real-life example. The manufacturer of an orchard mister decided to modernize the machine’s hydraulic circuit. The original circuit featured two fixed displacement pumps. One pump driving the mister fan. And the other pump driving the chemical pump.
In the … continue reading »