Hydraulic equipment reliability - begin with the end in mind - Part 2

In a previous article, I wrote about the advantages of defining your maintenance and reliability objectives for a piece of hydraulic equipment before you even order it. In response to this article, I received the following from one of our members:

"As an engineer for a heavy equipment manufacturer, I have to take exception with your advice in the last newsletter. I believe selecting a hydraulic oil, and then requesting the equipment manufacturer to design around that is putting the cart before the horse.

It makes much more sense for the equipment manufacturer to design the system for temperature, life, component availability, cost, and the million other things that go into machine design.

Would you tell Ford that you have a set of brake pads, and would like a car designed that could use them? No, you rely on the manufacturer to provide a system, and take their recommendation."

Hmmm... looks like I'm in trouble - again. I feel a bit like David, being pounded by Goliath. This member didn't reveal which OEM he works for... but the mind boggles with possibilities.

Needless to say, I don't agree with my colleague's assertion that the reliability-based strategy I advocated in last month's newsletter is "putting the cart before the horse". Let me explain with an example:

Say I am about to acquire a 25 ton hydraulic excavator. And let's say for example, this machine is fitted with Rexroth pumps and motors.

According to the pump manufacturer, optimum performance and service life will be achieved by maintaining oil viscosity in the range of 25 to 36 centistokes. I also know that in my location I expect to use a VG68 weight hydraulic oil and the brand of oil I use has a viscosity index of 95.

This being the case, Rexroth are telling me - indirectly of course, that if my new machine runs any hotter than 70 Celsius the performance and reliability of their pumps and motors will be less than ideal. Not only that, with 70 Celsius as the maximum operating temperature, the oil will last longer, the seals will last longer, the hoses will last longer and almost every lubricated component in the hydraulic system will last longer.

So being the sophisticated buyer that I am, I say to the OEM - before I order the machine: "I expect ambient temperatures at my location as high as 45 Celsius and under normal conditions (no abnormal heat load in the system) I want this machine to run no hotter than 70 Celsius. If you deliver it to site and it runs at 85 Celsius (or whatever) on a 45 Celsius day, then you'll have a problem on your hands."

I'm not suggesting this is in the interests of the OEM - clearly it's not. It's going to make their life more complicated and cut into their after sale revenue. No, it's totally in the interests of the guy signing the checks to keep the machine running. Luckily for all the OEM's out there, very few machine buyers will approach a new equipment acquisition with this level of sophistication.

If you enjoyed this article, you'll love Brendan Casey's Inside Hydraulics newsletter. It gives you real-life, how-to-do-it, nuts-and-bolts, hydraulics know-how -- information you can use today. Here's what a few members have said about it:

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