Fittings, Lubrication Fittings and Meter Units
Nomenclature of Fittings: Meter Units versus Control Units
The lubrication fittings used with both manual and automatic cyclic lubrication systems are referred to by as meter units. Each meter unit comes with a fixed orifice, a moving pin and an internal check valve. The orifice and pin size create the metering rate while the valve’s purpose is to insure precise discharge without loss of system priming between operating cycles.
Control units are lubrication fittings that act as proportioning devices in continuous lubricating systems. Each control unit proportions a continuous rate of flow to the bearings. The spiral opening in the control unit controls the rate of flow at each point.
Both types of fittings create flow resistance but the difference between these two types of lubrication fittings is that the meter unit uses a check valve so oil won’t drain back between lubrication cycles. Control units do not have check valves. This means that one shot or cyclic type lubricating systems require meter units while continuous lubrication systems require control units.
These fittings (meter and control units) can be mounted in any of the three basic configurations without affecting the operation.
- Straight – mounted at the bearing
- Tee Junction – mounted at the bearing
- Junction – removed from the bearing friction point
Fittings Flow Rate versus Flow Value
The flow rate of each lubrication fitting is stamped on the body of the unit. The flow rate of lubrication fittings describes the relative oil from the unit. Flow delivery from the unit doubles with each number increase. Each lubrication fitting is also stamped with an arrow to indicate the direction of flow.
The flow value is a relative numeric designation to refer to the oil permitted to flow through the lubrication fitting. It does not correlate to the volumetric discharge nor does it correlate to the amount of discharge on a unit/time basis.
Match Fittings to System Type
When designing a lubrication system, it is important to match the lubrication fittings to the type system. Proportioning devices with flow rates from 5/0 to 0 are recommended for continuous “loss” systems; a cyclic system requires 3/0 to 3; and a continuous re-circulating system 1 to 5.
Fittings come in 10 different sizes ranging from very slow discharge to very fast discharge. When designing a lubrication system, keep in mind that each increase in flow rate doubles the relative flow value, doubling the amount of oil that is delivered.