by Gary Alexander, CFPHS
Hydraulic reservoir accessories (or hydraulic tank accessories) can play a significant role in how well a hydraulic reservoir performs and to what degree fluid cleanliness is maintained.
A good hydraulic reservoir should have internal baffles situated in such a way that they prevent return line air from being drawn into the pump inlet. Baffles work to efficiently separate the return flow from the inlet flow. Additionally, baffles help the reservoir fluid circulate which promotes heat dissipation from the fluid.
In some cases a return line diffuser is a beneficial accessory and works to decelerate the returning fluid flow which prevents aeration of the reservoir oil due to turbulence. Reservoirs should also have risers or legs to keep the bottom of the reservoir away from the floor of the machine to which it is attached. These legs allow air circulation around all surfaces of the reservoir for increased heat dissipation.
Contamination is the single largest cause for hydraulic component failures, and keeping the dirt out of the hydraulic system is not an easy task. In addition to filters plumbed at critical points throughout the hydraulic system, contamination in the air around the reservoir must be considered. Airborne particles can enter the hydraulic reservoir and contaminate the oil if the reservoir is not totally enclosed. However, due to systemic oil level changes, a reservoir must “breathe”. As the fluid level in the reservoir changes due to cylinder travel, the reservoir must have a way to allow the air above the fluid to increase and decrease. Most commonly, an air breather-filter is used to prevent this ambient airborne contamination from entering the reservoir. This device is simply a replaceable air filter mounted on a port in the reservoir. It filters the air entering the reservoir, much like the air filter on an automobile engine.
In especially dirty environments, a specialized device such as a Parker KleenVent may be used. This device, a large rubber bladder in a metal shell, seals the reservoir while still allowing it to breathe. As the fluid level in the reservoir rises and falls, the clean air in the bladder is exchanged, rather than using the dirty ambient atmospheric air.
The fluid level in the hydraulic reservoir is also critical and must be monitored. Too much fluid and the reservoir may overflow; too little fluid and the pump may ingest damaging air rather than oil. Therefore, the minimum requirement is a visual sight glass that allows maintenance personnel to view the oil level at a glance. In many high production facilities, level switches are also used. These switches may be connected to warning lights or a machine shutdown circuit. This insures that the appropriate fluid level is maintained, while shutting down the system if the fluid level drops too low.
Finally, monitoring the fluid temperature is also an important part of fluid maintenance. Overheated oil can break down, lose lubricity, and cause premature component seal failure. A visual thermometer or temperature gauge is recommended and can be part of the fluid level sight gauge. Additionally, a temperature switch can be part of the level switch mechanism and connected to either a visual warning or system shutdown circuit.
The Fluid Power Specialists at Quality Hydraulics can provide further assistance in selecting hydraulic reservoir accessories.