Centrifugal Pump Fits & Clearance Checklist

May 1, 2003

 The following is a centrifugal pumps fits and clearance checklist. 

 

About the author:

Courtesy of the Hydraulic Institute Standards.

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 Centrifugal pumps fits and clearance checklist

No:

Measurement

Tolerance

1.

Ball bearing inside diameter (I. D.) to shaft

0.0001 in. to 0.0007 in. (0.003 mm to 0.018 mm) interference.

2.

Ball bearing outside diameter (O. D.) to housing

0.0001 in. to 0.001 in. (0.003 mm to 0.03 mm) clearance.

3.

Sleeve to shaft

0.001 in. to 0.0015 in. (0.03 mm to 0.04 mm) clearance.

4.

Impeller to shaft

Metal to metal fit to 0.0005 in. (0.13 mm) clearance.

Note: There are pumps such as horizontal, axial split pumps and multi-stage vertical pumps that have interference fits. Consult your OEM manual.

5.

Throat bushing

a)

Throat bushing to case

0.002 in. to 0.003 in. (0.05 mm to 0.08 mm) interference.

b)

Throat bushing to shaft

0.015 in. to 0.020 in. (0.40 mm to 0.51 mm) clearance.

c)

The throat bushings on some vertical in-line pumps act as clearances

intermediate bearings and require closer.

6.

Impeller

a)

Impeller ring to hub

0.002 in. to 0.003 in. (0.05 mm to 0.08 mm) interference.

The impeller ring is normally doweled or spot welded in at least two places.

b)

Impeller ring to case ring clearance

0.010 in. to 0.012 in. (0.254 mm to 0.3 mm) plus 0.001 in. (0.03 mm) per in. (25.4 mm) of impeller ring diameter up to a 12 in. (3,658 mm) ring. Add 0.0005 in. (0.013 mm) per inch (25.4 mm) of ring diameter over 12 in. (3,658 mm). For temp. ≥500 degrees (260°C) add 0.10 in. (2.54 mm). Also add 0.005 in. (0.127 mm) for galling materials (stainless steel).

c)

Renew impeller rings when clearance reaches twice original clearance

7.

Case rings

a)

Case rings are not to be bored out larger than 3% of original diameter

b)

Case ring to case

0.002 in. to 0.003 in. (0.05 mm to 0.08 mm) interference.

The case ring is normally doweled or spot welded in at least two places.

8.

Oil deflector to shaft

0.002 in. to 0.003 in. (0.05 mm to 0.08 mm) clearance. Install "O" ring in the ID if possible.

9.

Packing gland

a)

Packing gland to shaft

1/32 in. (0.8 mm) clearance.

b)

Packing gland to stuffing box bore

1/64 in. (0.016 mm) clearance.

10.

Lantern ring

 

a)

Lantern ring to shaft

0.015 in. to 0.020 in. (0.40 mm to 0.51 mm) clearance.

b)

Lantern ring to stuffing box

0.005 in. to 0.010 in. (0.13 mm to 0.25 mm) clearance.

11.

Coupling to shaft

Metal to metal to 0.0005 (0.013mm) clearance.

12.

Seal gland

a)

Seal gland alignment boss to stuffing box

0.002 in. to 0.004 in. (0.05 mm to 0.10 mm) clearance.

b)

Seal gland throttle bushing to shaft

0.018 in. to 0.020 in. (0.5 mm to 0.51 mm) clearance, unless otherwise specified for hot pumps.

13.

Seal locking collar to shaft

0.002 in. to 0.004 in. (0.05 mm to 0.10 mm) clearance

14.

Seal spring compression

7/8 in. (22.2 mm) long springs - 3/16 in. (4.8 mm).

 

1/2 in. (12.5 mm) long springs - 5/32 in. (4.0 mm)

Seal spring compression.

1/2 in. (12.7 mm) short springs - 1/16 in. (1.6 mm) unless otherwise specified by the manufacturer.

15.

Rotating and stationary seal rings

Sealing surfaces to be flat within 3 Helium light bands

16.

Heads, case, suction cover, bearing housing to case alignments fits

0.004 in. (0.01 mm) maximum clearance. Use dial indicator and feeler gauges to correct fit-up and alignment.

Horizontal axial split case

1. Stationary parts fit case metal to metal to 0.004" (0.01mm) clearance.

2. Measure and inspect case fits for wear and corrosion. Repair by building up and re-machining.

3. All other repairs same as vertical radial split case pumps except, case rings to be bored in a jig not chucked.

4. Align element in case with feeler gauges and dial indicator. Dowel bearing housing in place after alignment.

5. When cutting gaskets for horizontal split pumps, cut bolt hole openings on head and split gasket lengthwise. Cut the rest of the gasket on the case with all the slack in the boltholes pulled to the outside edges. Leave stuffing box gasket length long and trim after head has been set in place and tightened.

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OVERHUNG IMPELLER, SEPARATELY COUPLED, SINGLE STAGE, FRAME MOUNTED

1 Casing

18 Bearing, outboard

47 Seal, bearing cover, inboard

2 Impeller

19 Frame

49 Seal, bearing, cover, outboard

6 Shaft, pump

22 Locknut, bearing

67 Shim, frame liner

11 Cover, stuffing box

29 Ring, lantern

69 Lock washer

13 Packing

37 Cover, bearing

71 Adapter

16 Bearing, inboard

40 Deflector

73 Gasket

17 Gland

46 Key, coupling

This article was originally published on May 1, 2003 and has been revised for clarity.

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