How Much of a Hydraulic Tank Should You Paint?

pressurized hydraulic systems are dangerousA large part of being “smart” in any area of expertise comes from doing your homework. And this is especially true with hydraulics. Here’s a story from one of our members which illustrates this point:

“I’m fairly new to hydraulics and I thought coating the interior of a hydraulic tank I’d made with a zinc spray (cold galvanizing in a spray can, like paint) would be a good idea. The idea was fine but the reality was not so good. I had no way of predicting that the components of the oil would dissolve the zinc coating… I’m fortunate that there is little I could do at this point that would further endanger my soul.”

Call me superstitious, but I’m not a fan of painting the inside of hydraulic tanks, period. To digress for a moment, it reminds of a client a few years back who had a machine with a history of the oil to water heat exchanger failing and contaminating the hydraulic system with water. He asked me what he could do about the problem. When I suggested switching to an oil to air heat exchanger, there was a long pause on the other end of the phone. Followed by: “Why didn’t I think of that!”

Here’s the thing: engineer out potential problems if you can. If you don’t use an oil to water heat exchanger, cooling water can never contaminate the oil. If you don’t install pump intake isolation valves, the pump will never be started with the valve closed. And if you don’t paint the inside of hydraulic tanks, the paint can never come off.

Oh sure, all of these thing can be done in such a way that the risk of the worst case scenario happening is minimized. You can specify a double-walled oil to water heat exchanger. You can install proximity switches and interlocks on pump intake isolation valves. And there are paints specially formulated to withstand contact with the myriad of different hydraulic oils out there. Although as far as I’m aware they don’t come with a guarantee. Like I said, the worst case scenario is minimized, but NOT completely eliminated. The risk remains.

And why should you need to paint the inside of a hydraulic tank anyway? Think about it for a moment. How many other hydraulic components are painted internally? None. Zilch. Nada. So why don’t these components rust? Because the hydraulic oil is formulated with rust inhibitors.

But the hydraulic tank is different, right? I mean water settles to the bottom and air circulates in the top. Well, make sure the tank has a drain point – and see that it’s used. And if you install a desiccant breather, rust on the inside of the tank’s air space will be minimized, if not eliminated.

And so what if a bit of light rust forms on the inside of the tank anyway? Aside from not looking real pretty how bad can it be? It will likely make a small contribution to contamination load – probably in the sub 5-micron range. The filters will soon take care of this. And unless it’s a critical system with servo valves, no great cause for concern.

I’ve designed and built hundreds of hydraulic power units. And never painted the inside of a single tank. In some instances, I’ve actively discouraged it. I’ve also worked on many hundreds more built by others. And I’d guesstimate less than two percent of those had the inside of their tanks painted – some successfully and some not.

Either way, I’m yet to see any evidence that leaving the inside of a hydraulic tank unpainted is detrimental to the system. But as this member found out the hard way, painting it can be a costly mistake. And to discover six other costly mistakes you want to be sure to avoid with your hydraulic equipment, get “Six Costly Mistakes Most Hydraulics Users Make… And How You Can Avoid Them!” available for FREE download here.

5 thoughts on “How Much of a Hydraulic Tank Should You Paint?

  1. i will have to agree here by not painting the inside of a hydraulic tank , Ive seen its ones with red oxide and there were serious contamination .

  2. From my experience, I’ve never come across a hydraulic tank with the inside painted. I think it’s a bad idea painting the inside of a hydraulic tank as it increases the risk of contamination for the pump and valve seals.

  3. Well the whole idea is to keep your system at the proper level and to maintain the correct operating hyd oil temperature!!
    If you are adding oil to your system this will become an issue down the line, leak will get worse and running system below the proper levels will cost you parts and down time!-
    If your system is running at a higher temperatures this is a great clue that your system is not operating properly. Continue to run your equipment this way will shorten your equipments life span very quickly!! Heat will be the death to your hyd system!!
    Remember, heat and leaks will be no treat!!!!

  4. What way should the steel be cleaned after fabrication before the oil goes in? We are debating whether shot blasting completed hydraulic tanks is a good idea or not as there could be contamination that’s really difficult to get rid of.

    • If practical, hot caustic bath. This eliminates the residual shot from blasting, which as you say can be difficult to get rid of entirely.

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