A couple of days ago I had an interesting conversation with a person responsible for the preventive maintenance of a large number of hydraulic rigs. The guy is a very good and efficient mechanic, but he avoids repaired pumps like the plague, and so far I haven't been able to convince him otherwise.
It's not that I mind selling new pumps instead of repairs - no, the client's happy, we are happy, the machinery is happy. It's all fine and dandy. I just find the fact that he doesn't even want to give the repairs a try to be a bit too radical.
Normally when we touch on the subject of pump and motor repairs it goes like: "Repaired pumps are evil!" - "No, they are not!" - "Evil!" - "Not Evil!" - "Evil!" - "Not Evil!" - "Why?" - "Because they always break!" - "Why?" - "Because they always break!".. and so forth...
This last time the conversation took a different route - and raised a valuable point which I believe should be looked at. The background story was the same as always. The man received an overhauled pump from the main warehouse (I don't have any information about who did the overhaul or what kind of repairs had been performed on the pump) and the pump worked with a "strange noise" for about an hour before "completely losing pressure".
Although it is impossible to conclude what exactly caused the "meltdown" without studying the damaged parts, the mechanic did bring up an interesting fact - he said that whenever he received an overhauled pump, he never got it in a "properly conserved" condition. The pump would often come with main ports open, or at best would carry these flimsy plastic covers that didn't actually plug anything - in contrast to brand new Rexroth units that he always got properly sealed with metal plates and gaskets on the SAE ports and metallic or high-quality plastic threaded plugs in the respective drain and LS ports.
His point was - it is impossible for a repaired pump to survive long storage if it is not properly sealed by the repair shop - sooner or later moisture will find itself in and cause rust spots, which will cause the pump to fail prematurely. And he had never received a repaired pump that was properly sealed.
And you know what - that got me thinking... Neither have I. Seriously - around here - I haven't... Of course - when a client brings in a pump with proper plugs and covers - I overhaul it and deliver back with the same plugs it came in. But I can't say that I know of a shop around here that purposefully installs decent new plugs on repaired components all the time.
I always make sure I don't leave open ports on big industrial projects - experience taught me not to do that (what exactly do they say about people who learn from their own mistakes?...) Last time I did something like this involved gigantic and very expensive valve manifolds, and I still remember ordering about 1000 eur of SAE, BSP and Metric plugs to make sure the manifolds survive the short time storage and installation in unknown conditions.
But for "everyday" pump and motor repairs what I normally use is plastic caps for ports and film to wrap the whole unit in the end. It has worked so far - but I admit that I have certain doubts about how adequate this type of conservation would be for long-time storage in a "less than ideal" environment.
I have been in many industrial warehouses and storage areas - and very few of them have conditions appropriate for long term rust-free storage of metallic things. And there is no doubt that an "open" unit can suffer from spot rust damage due to condensation or even direct ingress of water into the casing. Plus - in case of industrial installations the water droplets that enter in contact with the pump can be contaminated with all sorts of corrosive chemicals. Underground storage areas are notorious for that.
Oh, and let us not forget about transportation. You can store your "unplugged" pump in the best storage facility in the world - and it wouldn't matter much because it spent a couple of hours under the rain in the back of an open truck, or had something extremely chemical accidentally spilled over it.
I can think of many other ways an "unplugged" unit can suffer damage during storage (flora and fauna, for one...) - but that's not the point. The point is - if a recently repaired pump is not going to be recommissioned right away, certain additional cares should be taken to make sure that it survives storage problem-free.
So, for pump owners:
When you buy a new hydraulic pump or a motor - make sure you keep all of these plugs and covers, and when you send it to a repair shop - make sure that it goes there with all the ports plugged. First of all - the shop will be more than happy to get a unit that's not pouring oil on the shop floor when they hoist it, and second - they won't have to look for plugs when they finish the repair. It's a win-win.
Second - when you get the pump back, most likely it's not filled with oil, so if you intend to store it, make sure you fill the case with clean hydraulic oil (no need to fill it "up to the brim", if the rotary group is "under" - you're OK).
If you got the pump with no plugs and covers - get proper metallic SAE covers with gaskets and "real" plugs and make sure you store the unit with the ports plugged.
It's not a bad idea to put the pump in a plastic bag, throw in a couple of moisture-absorbing bags, and then seal it.
For shop owners:
If you live in a perfect world and there is a rainbow in your window every day - just deliver an overhauled pump with proper plugs and covers every time you repair one.
If you live in a normal world - you can ask the client (preferably before you quote the repair) if the pump is going to be stored. Most of the times it won't, so you don't have to worry about storage precautions at all (within reason), but if it is - just include the necessary covers in your quote (or ask if they would want you to) - it's the best thing you can do for the pump, the client and your reputation.
TLDR: It is important to understand that in the real world, a perfectly good pump that is stored incorrectly can go bad. And while it is much less likely to happen to a new unit due to the fact that it had been tested on a factory stand and therefore already has an oil film on the internal parts, and is supplied with proper caps and plugs in all ports, it is very likely to happen to an overhauled pump because it won't have the same quality of "conservation".
Pumps are expensive, you know... When you store an apple and it goes bad - you throw it away and you're done. If you store a pump and it goes bad - rest assured that you're miles away from done!