Anybody who wants only one grade of stainless in a system plus additional inert polymer parts can be sure that galvanic corrosion will not take place over an extended period. All dissimilar metals have a potential difference between them in the presence of an electrolyte. Some combinations result in very destructive corrosion. Using a single material throughout addresses this problem. In an oil system with very low water content, galvanic corrosion isn’t going to be a problem for wetted parts but may be so for eternal parts open to the external environment where rainwater, condensation or seawater spray could be the electrolyte. Move to water hydraulics or systems using water-based fluids such as glycols and you have very real long term corrosion risks. In a complex system, one “rogue” fitting somewhere in the system could corrode due to another grade of material somewhere else within the wetted parts. That could result in system failure or simply being unable to dismantle or adjust a system component.
Anybody who has a safety critical system such as a nuclear installation won’t risk a wide mix of materials if water or water-based fluids are the hydraulic medium. Other users worry about deterioration of fluids causing corrosion over a long period. Although they may be offered individual components manufactured from a variety of very low corrosion metals, they simply won’t build a system using them as that nagging doubt is always there that over time, there will be galvanic corrosion. The downside with a nuclear system is massive and the risk totally unacceptable. Lots of our customers will specify our MW series pump manufactured from 316 grade stainless with small amounts of bronze and stainless 302/303/304/420/431. They are widely used and meet most requirements. Move to a requirement for 100% 316 stainless plus inert polymer and look at our Micropac 316 system builder parts.
There are particular design challenges in 100% 316 stainless and polymer hydraulics. Any normal mechanical design will use a variety of materials each with their own properties and benefits to achieve the overall design objective. For example, rotating or sliding parts will inevitably use bearing materials to cut friction and reduce wear. Running like material on like for large numbers of cycles or at high loads is always problematic. 316 stainless is not a particularly hard material and in addition to wear, it exhibits galling or cold welding. It will simply seize up. 316 stainless is an austenitic stainless steel and as such cannot be hardened by heat treatment. That presents basic problems in any design that relies on the hardening of parts to provide wear resistance. 316 stainless can however be work hardened as in processes such as roller burnishing, which can be helpful to a designer. A designer who has the objective of producing a 100% 316 stainless and polymer component is unlikely to be able to simply replicate a legacy design and substitute the new materials. Some parts such as ball check valves using metal on metal seats simply won’t work in 316 stainless. A ball would indent. A designer would move to poppet or soft seat valves. Polymer components will provide soft seating and low wear sliding parts. The same is true with pivots and bearings. Careful design will allow a designer to incorporate polymer bearings into parts. Sarum Hydraulics specialises in 316 stainless design.
We buy in components for 316 systems and have our own take. We would say that quality parts from reputable manufacturers and are nice to work with are our top requirement. Years ago, we decided that we would only use Swagelok double ferrule fittings because they are of a dependable quality and always a pleasure to work with. Read our white paper on single and double ferrule fittings. If you are building a system, it has to go together well. We rate serviceability highly in designing our own kit and on any bought in parts. Service kits have to be readily available, easy to fit and a fair price. If you are buying in a bill of materials for a 316 stainless system, the costs will mount up very quickly and may end up enormous. Value for money has to be a big consideration. Finally, we have always believed that needing to use multiple fittings to make one connection is not good news. It bulks out the space envelope, adds to cost and gives you extra leak paths. Better to use single-piece fittings if you can, hence our manufacturing our own over the years. We are an ISO9001 UK manufacturer and all our 316 stainless is from an EU or US mill. In summary, we build into our own equipment what we believe is important to designers and specifiers the world over.
Our PPS 316 stainless system builder range includes just three models of a very simple component hand pump with a minimal space envelope that would be piped into a system. These very compact Micropac PPS series hand pumps provide simple and inexpensive manual power with inlet and outlet check valves. A large range of 316 stainless inlet and outlet adaptors are offered if you can’t pipe directly to the standard ports. These units can be supplied with Swagelok double ferrule fittings to provide a very compact hand pump for piped systems. We manufacture three models with displacements up to 11cc/stroke single acting and pressures to 400 bar.
We also offer our Micropac MU series double acting hand pump providing 25cc/stroke double acting to 207 bar. This unit provides the benefit of double acting pumping on the up and down strokes although is inevitably larger than the very compact PPS series.
Our third specialist 100% 316 stainless hand pump range is the Micropac MB series Low Pressure hand pump, providing 100cc per double stroke up to 50 bar. This is available as a drum pump screwing into the standard BSP drain bung on a 207 litre drum, a panel mounted Low Pressure pump or a Low Pressure pump mounted using an angle bracket that we supply.
Our comprehensive range of 100% 316 stainless steel 250 micron strainer filters/breathers are an invaluable resource for a range of designers and specifiers. A range of hose tails and standpipes are available at reasonable prices.
We manufacture 316 stainless fittings where we haven’t been able to source one and we won’t specify bulky and leak prone multiple adaptors when one is optimum. This is a useful resource for 316 stainless system designers and specifiers. The section also includes our own NATO swivel adaptors for 10-32UNS filling and charging nipples.
Contact us to discuss your requirements.