Service Tips -- Care and feeding of hydraulic systems

Which hydraulic oil is right for hydraulic power units and pump systems? It depends…

It shouldn’t shock you that hydraulic fluid is the lifeblood of the hydraulic pump, hydraulic reservoir and perhaps most importantly, the hydraulic motor on a Hydra-Tech submersible dewatering pump, or in any hydraulic system.

Q&A -- Hydraulic systems

Q: What is the difference between a fixed hydraulic pump and a variable hydraulic pump?

A: Hydra-Tech pumps use a variety of hydraulic pumps on its hydraulic power units and the choice of a pump is typically determined by the customers’ application.

Fixed-displacement pumps include gear, vane and some piston hydraulic pumps. They deliver the same displacement per revolution and cannot be adjusted. Output adjustment with a fixed displacement pump is accomplished only with engine speed.

Variable-displacement pumps are piston hydraulic pumps that can be adjusted to provide a range of flows and pressures, which is determined and limited by the horsepower of the engine or motor that is driving it.

If a hydraulic power unit (HPU) will be running multiple pumps or other hydraulic tools with a range of hydraulic requirements, having a variable-displacement piston pump on your HPU is essential. A typical 74 horsepower diesel engine-powered HPU with a variable displacement pump would be set up at Hydra-Tech pumps for 30 gpm @ 2,900 psi. Several Hydra-Tech pumps run at this flow and pressure, but if you had a pump or hydraulic tool that had a maximum flow and pressure of, for example, 20 gpm @ 2,700 psi, these pumps allow users to reset the piston pump on the HPU to run at that volume and pressure.

This adjustment alters the geometry of the displacement chamber, which in turn affects the flow and pressure the pump delivers.

This change requires a flow meter and some hand tools; it is not something done by simply turning a knob or adjusting a setting in a control panel.

Q: I want to source my own hydraulic hoses. What should I look for?

A: This applies specifically to the hydraulic hoses used to connect the pressure and return ports of the hydraulic power unit (HPU) to the pump. To replace a hydraulic line on the HPU itself, refer to the hose needing replacement or consult with the factory to assure the correct hose is selected.

There are many options when it comes to hydraulic hoses. There are 16 different SAE standards with some additional options within some of those 16 SAE standards. Originally, there were 19 SAE standards but three, 100R9 through 100R11, are no longer a part of the standard.

Most of the options from standard to standard are related to the following parameters:

  • Size
  • Type of hydraulic fluid being used
  • Working pressure (pressure rating)
  • Temperature rating
  • Physical makeup of outer cover (resistance to ultraviolet light, chemicals abrasion and other characteristics)
  • Type of end fittings that will be used and whether fitting installation requires skiving (removal of outer casing of hose) before installation
  • Conductive/nonconductive

Most of the systems that Hydra-Tech Pumps manufactures don’t exceed 3,000 psi, so Hydra-Tech offers 100R12 and 100R17 hydraulic hose rated for 3,000 psi with abrasion-resistant covers. These hoses offer a good mix of safety, durability, wear and UV resistance; they are good general purpose hoses for use with hydraulic pumps and hydraulic power units.

Hydraulic hoses are stamped with specifications on the outer covering and can be used to help identify the correct replacement hose.

Which hydraulic oil should be used to fill the reservoir on a new hydraulic power unit? Whether you’re using a
6 horsepower or a 400 horsepower hydraulic power unit (HPU), the choice of hydraulic oil is the same for both, but the volume required to fill it will vary significantly.

For example, for Hydra-Tech’s gas and diesel hydraulic power units of less than 15 horsepower, Dexron ATF is recommended. This hydraulic oil offers a wide temperature range and excellent wear properties.

All hydraulic power units greater than 15 horsepower require AW46 hydraulic fluid in the reservoir and lines. This 20-weight (ISO46) hydraulic oil has anti-wear (AW) additives and is designed for normal climates. In colder climates, Hydra-Tech recommends using 10 weight (ISO 32) or AW-32 hydraulic oil.

Environmental considerations
If the HPU will be used around lakes, streams or other environmentally sensitive areas, biodegradable hydraulic oil should be used in the system. Most manufacturers offer either a mineral-based oil such as Chevron Clarity or vegetable-based oil such as Mobil EAL224H.

Clean hydraulic oil is as important to your hydraulic power unit as clean engine oil is to the engine. Simple steps such as wiping and cleaning quick-disconnects with a clean rag can prevent dirt and debris from entering the hydraulic fluid system. Always follow the recommendations in the operator’s manual when it comes to service intervals related to the hydraulic system.

 In general:

  • Change the hydraulic return line filter every 250 hours.
  • Change the hydraulic oil every 600 hours (larger models 1,000 hours).
  • Hydraulic reservoirs have a suction strainer with an integral magnet to catch any metal that might get into the system. When changing the hydraulic oil and the reservoir is empty, remove the suction strainer and thoroughly clean it, including removing any metal debris from the magnet. Once cleaned, rinse with mineral spirits and properly reinstall it.

These are general suggestions for most hydraulic power units; consult the operator’s manual for the recommended service intervals for these critical hydraulic system components.

Dirt or debris in a hydraulic system can damage or destroy components in the hydraulic pump on the HPU as well as the hydraulic motor on a hydraulic-powered submersible pump. Hydraulic oil is the lifeblood of your system – make sure to keep it clean for a long and reliable service life.


This article originally appeared in the July-August 2022 issue of Pro Contractor Rentals magazine. ©2022 Urbain Communications LLC. All rights reserved.