JPUJournal pad units

Check both starting and running radial loads, choose a shaft diameter and journal length that fit the machine, then check the operating-speed zone for the selected L/D ratio.

The running load on a pad and the running load between pads are separate conditions. Journal pressure is based on the projected area: nominal shaft diameter A multiplied by pad length B.

Starting pressure basis

2.0 MPa.

Running pressure basis, load on pad

2.2 MPa.

Running pressure basis, load between pads

2.8 MPa.

Performance-curve oil conditions

ISO VG 32; inlet 45°C; outlet 62°C.

• For speeds outside the indicated operating zone, or a different oil grade or temperature, request a duty-specific assessment, including power loss and oil quantity.

The pad working face has a preload profile that forms a converging hydrodynamic oil wedge, including under light loads. The nominal radial clearance at the pivot is Cpiv; the radial pad-bore clearance is Cpad.

Preload = 1 − (Cpiv / Cpad) = B / (A + B). Its average value is 0.6 for the standard range when the shaft diameter is within the specified normal- or large-clearance limits. The diagram assumes the shaft is concentric with the housing and the pad has no tilt; Cpiv is half the diametric clearance CD.

In the preload geometry, A = Cpiv and Cpad = A + B. These diagram letters describe clearances and are separate from the size-table symbols A for nominal shaft diameter and B for pad axial length.

The normal-clearance arrangement is recommended for oil-film stiffness. Large clearance is intended for pad-temperature difficulties at very high speeds and unit loads and requires discussion with our engineers.

Shaft journal surface finish

0.4 µm Ra (N5).

• The bore remains nominal and the diametric clearance is taken from the shaft. Normal and large clearances have separate absolute lower and upper shaft-diameter limits; do not interpret them as signed deviations or interchange them.

Provide the required oil quantity at the specified inlet temperature. For high-speed units fitted with TT thrust-pad endplates, directed lubrication feeds the thrust-pad leading edges and allows hot oil to drain freely; the supply pressure at the bearing should generally be at least 0.5 bar.

Standard supply pressure

0.5–1.0 bar at the oil-distribution annulus.

Filtration before the bearing

Better than 25 µm; where possible, 10–15 µm.

Lubricant quality

Good-quality mineral oil inhibited against oxidation, corrosion and foaming.

Pad-temperature monitoring

Thermocouples or resistance temperature detectors can be fitted to the journal pads.

• High-pressure jacking oil is advisable when stationary journal pressure exceeds 2.0 MPa. The starting-load guidance describes this provision for shaft diameters of 100 mm and above; specify it for engineering assessment.

The reference comprises JPU, the nominal journal bore, the pad axial length B, and the endplate letters for the two ends.

B / BB

Fixed end baffles; BB has a baffle at both ends.

F / FF

Floating seals carried by steel endplates; FF has a floating seal at both ends.

L / LL

Whitemetal axial-location faces, normally used during run-up and run-down; LL has location faces at both ends.

T / TT

Endplates retaining pivoting thrust pads for specified axial loading; TT has thrust-pad arrangements at both ends.

• Different endplates can be specified at the two ends. Special lengths, mounting flanges and offset journal pads are engineering options that require confirmation.
• For thrust-pad endplates, state the normal, starting, peak and overspeed thrust loads and their directions. A radial load rating does not establish the axial capacity of an endplate arrangement.

DIN and ASTM materials are approximate equivalents; differences in composition can exist. Screw threads follow ISO metric standards.

Housing and journal-pad steel

BS 970-070 M20 / Werkstoff No. 1,0724 / ASTM A576 AISI C1022.

Journal-pad whitemetal

BS 3332/C / DIN 1703 LgSn89 / ASTM B23 GR2.

B-series endplates

Gunmetal: BS 1400-G1 / DIN 17656 GB Rg 10 / ASTM B143/1A.

F-series endplates

Steel: BS 4360 GRD 43A / ASTM A284 GRB.

F-series floating seals

Leaded bronze: BS 1400-LB4 / DIN 1716 GSnPbBz 10 / ASTM B144/3C.

Journal-pad stops

Steel: BS 970 080 M40 / DIN 39 Mn4 / SAE 1040.

Bearing stop

Case-hardened steel: BS 970-214 M15 / DIN 12 Mn6 / SAE 1116.

Oil-restriction plugs

Brass: BS 2874-CZ121M / DIN CuZn40Pb3 / ASTM B-21C.