Wouldn’t it be great to top up your hydraulic system from the tap?

Some industries do this. They pay the extra cost of the system components from Danfoss or Tony Markham at the Water Hydraulic Company and use water. Some industries like mining or steel-making find water essential for safety reasons. Pressure testers like it because it is cheap and does not contaminate their systems. If there is a leak, there is not the contamination issue that oil brings.

Some industries cannot use mineral oil, yet get round this by using another fluid such as, like the food industry, vegetable oils. Other people sidestep the issue completely and use electric drives, dare I say it.

Much as water is the ultimate eco friendly fluid, it has some downsides.

Water is poor on lubricity as it does not provide much lubrication between two surfaces. In contrast, mineral oil does. You can engineer your pumps and motors to include self lubricating bearings, but at a cost. Some designs are just fundamentally unsuitable for water for this reason, even before you move on to other problems. Once you add wear additives, you are back to something that may not be so friendly to the environment. In the limit, the fluid may end up being as tricky as oil for disposal but be questionable on long term stability which in turn may provide the required lubricity.

As well as lubricity, the low viscosity of water also immediately brings problems with leakage compared to oil where you are using a spool with a fit in a bore. The sort of hydraulic spool valve that is suitable for oil will certainly have to be replaced with a different design for water application. Oil hydraulics uses massive numbers of very versatile spool valves at low cost. Water hydraulics can’t compete easily yet.

Keeping an eye on the stability of the fluid if you are using additives is quite an issue. If water evaporates, the concentration of the additives will rise, which may be less than ideal. The fluid needs more maintenance than mineral oil. Oil hydraulic systems can be massively abused on the condition of the oil, I think, although it catches up with people eventually. In comparison, a water additive system needs care. That said, mineral oil absorbs water over time with long term implications on corrosion and wear.

Leave water for a relatively short time and you get bacterial growth. After a period, it may no longer be very healthy. If there is light, you will get algae. If you add biocides, again, you no longer have an eco-friendly fluid and furthermore you have something which could poison people.

A fluid which cannot work below freezing point is rather a menace, particularly if it becomes solid, expands and can damage pipes and chambers.  Add ethylene glycol based anti freeze compounds and you can again end up with something quite nasty.

Water can be quite corrosive, so if you need to add anti corrosive additives, you have moved away from your pure fluid.

In reality, additives used to enhance one property can give rise to another problem. For example, many users are terrified of water glycols left for periods in aluminium alloy components due to corrosion.

All this said, an additive to the water will be in a low concentration, not a “full on” highly unfriendly fluid like mineral oil. If you are able to use non toxic and bio degradable additives, then that changes the game quite substantially. Additives can only develop to become better, so the future is bright for water hydraulics.

At Sarum Hydraulics, we love water for pressure testing. Our pumps thrive on it for year after year. Lucky us! For other applications, I think that water is still the more difficult option. I am sure that we will continue to see growth in the market. I am surprised the number of enquiries that we have had over the years where the customer has had a genuine desire to use water but ended up opting for oil. Maybe things will change over time and more mainstream water systems will be used. Some challenges you can get over. Others are inherent and are both the best and worst thing about water.