Originally Posted by gjordan
Andrew, several years ago, I asked a friend who did a lot of hydraulic work about a hydraulic starter/pump and he said that the pumps werent designed to be used as motors
. Of course there may be specialized ones that he (and I) were not aware of, but my idea was to just use a hydraulic motor
with a conventional bendix in place of the electric
Hmm - some pumps are, most aren't. In a few cases which are not, you can nevertheless specifically order a pump variant which will explicitly serve dual (motor & pump) duties.
DC generators are not usually designed to double as motors, either, but will generally handle short spells of motor duty, sometimes indefinitely.
And similarly with hydraulics: even some of those not designed for dual use will not be damaged by occasional 'off-label' duty, especially at low torque. The guys who sell them invariably recommend against it, but they've nothing to lose by overstating their case:
expert advice always
assumes idiotic customers, with good reason, because that's when it bites them in the bum. And in any case they would prefer to sell two units rather than one.
Be that as it may: I'm pretty sure Lance Armstrong could start a 2GM
, and he's only good for 0.7kW, I believe. My pumps are good for at least an order of magnitude more than that.
on eBay, one does not have the luxury of specifying a special build of a given pump, hence my plan to feel my way into it by disassembling, checking how the sealing cheek-plates are energised, what the implications are for case drains, and all the usual reasons why it might be a problem.
If all seems "good to go" I would then carry out some test starting with no load, and low pressure, and see if anything untoward seemed to be signalled.
I would not consider this for other than emergency
I certainly did toy with the idea of a hydraulic motor as a substitute for electric
, (with Bendix etc) but for reasons including (but not limited to) those I gave above, I think I probably won't go to that extra trouble. [One reason against not spelled out above: It offers greater reliability
but reduced redundancy].
There are, as others have noted, hydraulic starters available off the shelf, although not generally for such small motors. There are also 'windup' starter motors, effectively heavy duty clockwork! available for many diesels, and in this case, they go quite small because they're ideal for the engines fitted to lifeboats.
Having said all this I thank you again for bringing your ideas forward and probing for weaknesses in mine: it's great to revisit these things, and you've reminded me that I may need to rethink the whole notion if my pumps do turn out unsuitable for emergency
Anybody who knows lots about this specific issue, please feel free to chime in>
I much prefer to know I'm wrong than to think I'm right.