By Brendan Casey,
Transmission pump failure caused by insufficient charge pressure on start-up.
An article in the New England Journal of Medicine reported that the adoption of a simple operating room checklist developed by the World Health Organization (WHO) reduces post-op death rates by 40% and major complications by more than a third. (Important note: If you ever have to undergo major surgery, make sure the surgeon will be using this checklist before you give consent.)
I didn’t find this study’s results surprising. After all, checklists are meant to remove all margin for error and omission. It’s why commercial pilots and professional divers use them. It’s why I’m a big advocate of their use when commissioning or re-commissioning hydraulic systems to avoid damaging components during startup.
Botched procedure causes failure
Anecdotal evidence gained through my many years working in the hydraulics repair industry suggests that the failure of maintenance personnel to follow proper procedures when re-starting hydraulic systems after carrying out maintenance work is a significant cause of “infant mortality” in hydraulic equipment.
If the right steps aren’t followed during initial start-up, hydraulic components can be compromised. Incorrect commissioning can cause damage from cavitation, aeration, and inadequate lubrication. In many cases, the component may work for a while, but the harm done at startup dooms it to premature failure — hundreds or even thousands of service hours after the event.
Unless you’ve worked in the hydraulics repair business, you’d likely be amazed at the number of failures that wrongly end up as warranty claims. And it’s frustrating for everyone concerned because they’re totally preventable.
Select figure to enlarge.
For example, a new client, a hydraulic repairer, recently consulted me about a piston pump rebulid failure. The pump was not installed by them, but when the failed unit came back for inspection, it was obvious the drive coupling had been hammered onto the pump’s drive shaft.
(For the uninitiated, this is a really dumb thing to do. When a coupling is tight on its shaft, do not reach for a hammer — reach for the emery paper and get busy with it. This applies to any piece of rotating equipment, not just a hydraulic pump or motor).
Of course, my client was interested to know what influence the battering of the pump’s drive shaft had on its failure. That’s a story beyond the scope of this article. But part of my advice was to supply a commissioning procedure checklist with every hydraulic component rebuild.
All hydraulic repairers should do this to avoid unnecessary infant mortalities and the warranty claims that usually result from them. I instigated their use at the hydraulic repair shop I managed more than 15 years ago and I advocate all hydraulic equipment users adopt them in my book, Insider Secrets to Hydraulics.
But now there’s even a book entirely about checklists: The Checklist Manifesto by a surgeon who insists that costly human error in everything would plummet if checklists were forced on everybody — for everything.
Checklists for everything may be taking it a tad too far, but when the cost of mistake or omission is significant, it is perfectly reasonable and sensible. In the case of hydraulic equipment, the cost of mistake or omission can manifest itself in ways other than premature failure of components.
For example, I recently reviewed the events that led to a lawsuit against a company that carried out maintenance work on an aerial work platform prior to a worker being injured using it. Had the company’s technician followed and documented procedures outlined in the machine’s manual before handing the machine back to its operator, his company would not have been a defendant in the matter.
Make it easy to remember
There are two parts to getting this right: knowing what to do and remembering to do it. If you don’t know what to do, that’s one thing. But if you do know, but forget to do it, that is soul destroying. You can’t pat yourself on the back for filling the pump housing with clean oil if you forgot to open the intake isolation valve before starting the engine!
A well thought-out checklist will prompt you to do the things you might otherwise forget: like connecting the case drain line.
Mistakes like this are prevented by using a checklist. I don’t like relying too much on memory, so even after 20+ years working on hydraulic equipment, I would never attempt to commission or re-commission a hydraulic system without having a piece of paper to remind me of what I need to do and the order in which I need to do it. This simple discipline eliminates all possibility of mistake.
Make the most of your checklist
Issues do exist with checklists when it comes to their effectiveness. The first is that to be most effective they need to be machine specific. The pre-flight checklist for a Boeing 747 is no use to the pilot of an Airbus A380.
You can cover the steps common to all situations, such as in the case of a piston pump, “fill the case with clean oil through the uppermost drain port.” But beyond that, so many different variants of pump installation exist, it’s nearly impossible — and potentially confusing — to try to cover all necessary steps in a single, generic procedure.
The second point is that the best checklists are dynamic; they’re a work in progress. A friend of mine, who is ex-military, uses a checklist before embarking on a camping trip with his family so he doesn’t leave anything essential at home. But he takes this one step further. When he returns, he updates his checklist. Not only does he add items to his list he should have taken but didn’t, he also removes from his list things he did take but did not require.
The point about this is when you sit down to write a checklist, it is difficult to foresee every eventuality — not only things that should be done but also things that should not be done.For example, my previous, pre-start checklists did not include the instruction: “Do not force the drive coupling onto the pump or motor shaft!” But they will now. And so should yours.
The best thing about checklists — and something the New England Journal of Medicine was quick to point out — is there is virtually zero expense associated with their adoption and use. Which is why no hospital — or hydraulic equipment user — can use cost as an excuse for not using them.
And in case you’re thinking my analogy between medical surgery and hydraulic component change-outs is a bit tenuous, consider this: From the WHO checklist (post-op):
“Confirm instrument, sponge and needle counts are correct.” Hydraulics translation:
“Did you remove the rag you stuffed into the pump intake line, before you connected it to the replacement pump?”
The consequences are different, but the outcome is similar: embarrassment, guilt, damaged reputation, cost — things we all want to avoid.
So never attempt (or allow anyone else to attempt) to start or re-start a hydraulic machine after changing components without a written checklist that tells you exactly what to do, and the order in which to do it in.
Brendan Casey has more than 20 years experience in the maintenance, repair, and overhaul of mobile and industrial hydraulic equipment. For information, visit www.hydraulicsupermarket.com.