Hydraulic System Design & Operation

Here are some important points to consider in designing and using hydraulic systems:

1. Never undersize the reservoir.  The excess reserve oil in a hydraulic system is to dissipate heat and prolong the life of the pump.  Over sizing the reservoir by 5 to 15 gallons will offer substantial benefits by allowing the hydraulic system to run cooler and extending the life of the system’s pump.
2. Air entrainment must be avoided in any hydraulic system.

To avoid air bubbles in the oil: 

1. Do not introduce returning oil above the minimum oil level.
2. Always keep hydraulic systems topped up and fix those leaks! System leaks lead to low oil levels which results in poor cooling and vortex related air entrainment.  Just like a draining bathtub, a vortex can form over the suction port when the surface of the reserve oil is too close to the port.  When air enters the system it causes pump cavitations, premature pump failure and spongy hydraulic operation.
3. The reservoir should have internal baffles to reduce sloshing and to prevent the hot returning oil from immediately entering the pump’s intake port.  This allows more heat to radiate as it takes a longer route in the tank.
4. Allow the reservoir to breathe. Adding an auxiliary ¾” vent on larger systems ensures good air exchange.

Plumbing: Although aluminum has many advantages over steel it will not tolerate flexing as well.  Support all valves and hoses that are connected to the reservoir.  If the overhanging weight of fixtures and piping causes the fitting to flex, the area around the fitting will fatigue and will eventually fail.  When installing your fittings into a fuel or hydraulic reservoir, be sure to support your plumbing. Anchor the plumbing to the same surface as the reservoir so the assembly moves in unison.  Mount the reservoir on a rigid surface, or use a spring mounting kit if mounting a reservoir “cross-chassis”.

Proper thread care is extremely important:

1. Do not over-tighten aluminum connections.  Hand-tighten, plus ¼ turn is all that is required. 
2. Do not engage cast iron fittings with the aluminum threads on the reservoir. The threads on cast iron fittings are rough and will tear the soft aluminum threads.  
3. When making a connection to a reservoir, be absolutely sure the first threads are engaged properly.  Forcing the connection may cross the threads and damage the soft aluminum.
4. When connecting steel to aluminum fittings use only the highest quality fittings.
5. Remember that you are making a connection with tapered threads.  Guard against over-tightening.  Excessive pressure exerted when making a connection can result in thread damage.  Always use anti-seize compound.  If you don’t, you may discover upon disassembly that even the best of fittings seize and tear out the threads.

Replace that damaged or missing breather cap. Never stuff a rag in the filler or breather port to substitute for a cap or breather.  This risks the introduction of contaminants into the fluid and is a potential fire hazard.

When topping up or filling the reservoir, use only clean hydraulic fluid of the grade recommended by the pump manufacturer.

We do not recommend dividing a fuel tank into part hydraulic and part diesel fuel. Most shops doing this work do not have access to the O.E.M. tank heads, so they cut a flat plate and weld it in place.  This increases the risk of fuel leaking into the hydraulic system, and vice-versa.  The potential for consequence is so great that some trailer owners will not connect their systems to this type of setup.  There is a correct method of building a split tank.  Propower will be pleased to discuss design questions about your hydraulic systems with you.

Never rework a fuel tank into a hydraulic tank.  Converting a used fuel tank can be cheaper than purchasing a proper hydraulic reservoir but it can create expensive problems for your system.  Those who perform these types of conversions will not take the time and effort to open the tank to install baffles or clean the interior correctly.  We have seen tanks that were not set up to breathe properly.  Some didn’t have anti-vortex plates or magnetic plugs installed.  Some were so dirty inside that the whole system was contaminated with weld spatter and filings from cutting in the added ports. Some had sludge from the diesel fuel. Some still had the “Diesel Only” filler caps in place!

Hydraulic systems primarily use reservoirs made from aluminum because they are light; release heat well, resist corrosion, and can be polished to a mirror finish if desired.  It is however, a very soft metal and requires special care to obtain optimum performance.  Following this guide will give your hydraulic system many years of trouble free service.