As mentioned in the introduction of the grease lubrication section, the bearing should initially be completely filled, while the free space in the housing should be partly filled. Depending on the intended method of replenishment, the following grease fill percentages for this free space in the housing are recommended:

–	40% when replenishing is made from the side of the bearing (fig 1);
–	20% when replenishing is made through the annular groove and lubrication holes in the bearing outer or inner ring (fig 2).

Suitable quantities for replenishment from the side of a bearing can be obtained from

G_p = 0,005 D B

and for replenishment through the bearing outer or inner ring from

G_p = 0,002 D B

To facilitate the supply of grease using a grease gun, a grease nipple must be provided on the housing. If contact seals are used, an exit hole in the housing should also be provided so that excessive amounts of grease will not build up in the space surrounding the bearing (fig 1) as this might cause a permanent increase in bearing temperature. The exit hole should be plugged when high-pressure water is used for cleaning.

The danger of excess grease collecting in the space surrounding the bearing and causing temperature peaks, with its detrimental effect on the grease as well as the bearing, is more pronounced when bearings operate at high speeds. In these cases it is advisable to use a grease escape valve rather than an exit hole. This prevents over-lubrication and allows relubrication to be performed while the machine is in operation. A grease escape valve consists basically of a disc that rotates with the shaft and which forms a narrow gap together with the housing end cover (fig 3). Excess and used grease are thrown out by the disc into an annular cavity and leaves the housing through an opening on the underside of the end cover. Additional information regarding the design and dimensioning of grease escape valves can be supplied on request.

To be sure that fresh grease actually reaches the bearing and replaces the old grease, the lubrication duct in the housing should either feed the grease adjacent to the outer ring side face (fig 1 and fig 4) or, better still, into the bearing. To facilitate efficient lubrication some bearing types, e.g. spherical roller bearings, are provided with an annular groove and/or lubrication holes in the outer or inner ring (fig 2 and fig 5).

To be effective in replacing old grease, it is important that grease is replenished while the machine is operating. In cases where the machine is not in operation, the bearing should be rotated during replenishment. When lubricating the bearing directly through the inner or outer ring, the fresh grease is most effective in replenishment; therefore, the amount of grease needed is reduced when compared with relubricating from the side. It is assumed that the lubrication ducts were already filled with grease during the mounting process. If not, a greater relubrication quantity during the first replenishment is needed to compensate for the empty ducts.

Where long lubrication ducts are used, check whether the grease can be adequately pumped at the prevailing ambient temperature.

The complete grease fill should be replaced when the free space in the housing can no longer accommodate additional grease, e.g. approximately above 75% of the housing free volume. When relubricating from the side and starting with 40% initial fill of the housing, the complete grease fill should be replaced after approximately five replenishments. Due to the lower initial fill of the housing and the reduced topping-up quantity during replenishment in the case of relubricating the bearing directly through inner or outer ring, renewal will only be required in exceptional cases.