Pressure Testing Applications
For pressure testing, our normal advice is to look seriously at water as a medium before moving to oil or other fluids. Testing on water has the benefits of low cost, external cleanliness in a workshop, internal cleanliness with no degreasing required, water being low viscosity, fairly searching and safety. There are few ancillary components in the system, so little cost implication on having to buy in water compatible components.
Water Hydraulic Applications
It would be fair to say that for the vast majority of power hydraulic applications, people will only move away from mineral oil because they have to for various reasons. There are a whole spectrum of fluids available, all having various pluses and minuses. Some water glycols offer properties very close to those of oil although check out the technical data carefully. Suppliers such as Vaughan have considerable expertise. Water glycols are also used as low viscosity offshore control fluids and these have their own characteristics. A further specialist class of fluids are phosphate esters such as Monsanto “Skydrol”, used as a fireproof hydraulic fluid for the aerospace sector. Finally, water is another option. We have considerable expertise on alternative fluids, so please ask.
Key issues to address when looking at alternatives to mineral oil are:
Inherent safety – You are using a fluid under pressure. Consider the fire risk if there is a leak. Also consider that some of these fluids are quite poisonous.
Cost – Some glycols may well be more expensive than mineral oil, whereas tap water is the perfect medium for low cost.
Corrosion – Materials of the equipment may need to be changed in response to different fluids. For pure water, stainless steel and bronze would be the best choice for a long service life. Anodised alloy can also provide a long service life, although brass should not be used for fittings (due to galvanic corrosion). Long term use of water glycol (such as anti-freeze) in conjunction with anodised alloy is also a concern for some industries due to corrosion. Hard water has its own scaling problem.
Lubricity – Pure water has poor lubricating properties compared with mineral oil, so components must be selected to take this into account. Composite seals used in many of our hand pumps work very well on water, but any bought in components using O rings in a dynamic sealing application can suffer. If other fluids are being assessed, the lubricity can sometimes be quite difficult to evaluate. Certainly, premature failure due to seal wear can limit the application of these alternative fluids. Some offer properties similar to oil.
Viscosity – Some alternative fluids offer viscosities comparable with mineral oil, but others are as thin as water. Mainstream hydraulic components for mineral oil often just cannot cope with thin fluids and specialist valves have to be sourced. Ball check valves seating on metal seats are generally not suitable for thin fluids and poppet valves should be considered. Relief valves need to be soft seat of similar construction. Directional control valves are unlikely to be mass market spool valves as they are simply unsuitable for water or low viscosity fluids.
Temperature range – Do not neglect the fact that water freezes! If you have to use additives to prevent freezing, there will be another set of decisions to be made.
Many of our pumps were designed for use on water so are true multi fluid units. Please contact us.