Rotary Vane Vacuum Pump Vanes: How to Measure Wear and When to Replace

Measure the height of every carbon vane with a caliper and compare the lowest reading with the minimum height the pump maker publishes for that model. When any vane reaches the minimum, change the whole set. On a Becker KDT 3.140 a new vane is 48 mm high and the limit is 31 mm. On an Elmo Rietschle KTA 140/4 it is 52 mm new and 38 mm minimum. On a Busch Seco SV 1040 it is 44 mm new and 33 mm minimum. Chips, cracks, diagonal wear or heavy cupping mean a new set regardless of height.

Why carbon vanes wear and which dimension to measure

A dry running rotary vane pump has an offset rotor with slots cut along its length. A carbon vane sits loose in each slot. As the rotor turns, centrifugal force throws the vanes out against the cylinder wall, and the pockets between them carry air from the inlet to the outlet. Busch describes its Seco vanes as self lubricating: there is no oil in the pump chamber, so the carbon itself is the bearing surface.

That contact wears the vane down a little on every revolution. The length does not change and the thickness changes very little. The height, measured from the edge that sits in the bottom of the slot to the bevelled edge that rides on the cylinder, is the dimension that shrinks. Becker's and Busch's service sheets call this dimension the "width", and Rietschle calls it height (X). It is the same measurement: the middle number in a size such as 240 x 48 x 4 mm.

Across the 25 carbon vane sets we list for Becker, Elmo Rietschle, Orion and Busch pumps, new vane heights run from 16 mm to 88 mm, lengths from 32 mm to 355 mm and thickness from 3 mm to 7 mm. Twelve of the 25 sets use 4 mm thick vanes. Because the range is so wide, there is no universal wear limit. It has to come from the data for your model.

How to measure vane wear

• Isolate the pump. Lock out the motor so it cannot start while the cover is off.
• Remove the end cover. On the Becker KVT, KDT and DVT range this means taking off the air guide cover and the M10 end shield bolts, then using two of the bolts in the jacking holes to pull the end shield. On a Rietschle KTA /4, take off the suction grid and draw the end cover with one of the cover bolts screwed into the centre of the bearing cover.
• Note the vane orientation before you pull them. The bevelled edge faces outward and follows the direction of rotation.
• Measure each vane at both ends and in the middle with a vernier or digital caliper. Use the lowest of the three readings.
• Compare against the minimum. Becker puts the minimum vane height on the maintenance sticker on the pump. The figures for four common models are in the chart below.
• Inspect the faces and edges. Look for chipping, one end lower than the other, scoring, and a hollowed face.

Write the readings down with the running hours. Two or three sets of readings give you a wear rate in mm per 1,000 hours, which tells you when the next set will be due far better than any fixed interval.

Published minimum heights for common pumps

These are the limits from each maker's service data, set against the new height of the matching vane set in our catalogue:

• Becker KDT 3.140: new 48 mm, minimum 31 mm. Vane set Becker 90133400004, 4 vanes 240 x 48 x 4 mm.
• Becker KDT 3.100: new 39 mm, minimum 26 mm. Vane set Becker 90133300004, 4 vanes 250 x 39 x 4 mm.
• Elmo Rietschle KTA 60/4 to KTA 140/4: minimum 38 mm (27 mm on the KTA 40 and KTA 50). The KTA 140 vane is 52 mm new: Elmo Rietschle 526627, 6 vanes 260 x 52 x 5 mm.
• Busch Seco SV 1040: new 44 mm, minimum 33 mm (27 mm on the SV 1010 and SV 1016). Vane set Busch 0722522488, 7 vanes 95 x 44 x 4 mm.

Put another way, these vanes are finished after losing 11 mm to 17 mm of height, or roughly a quarter to a third of what they started with. A vane that has gone from 48 mm to 40 mm on a KDT 3.140 still has 9 mm of life left. One at 32 mm is due now, even though it looks only a little shorter than new to the eye.

How often to check

The makers set different first checks:

• Becker KDT 3.100 and 3.140: check vanes every 3,000 hours, at the same visit as the dust separator element.
• Elmo Rietschle KTA /4: first check at 4,000 hours, then every 1,000 hours, or sooner as the height approaches the limit.
• Busch Seco SV: every six months, more often under severe operating conditions.

Treat these as the latest point for a first look, not as a replacement interval. A pump running hot, at high vacuum, or cycling on and off all day will reach the limit well before a pump on light duty.

Signs the vanes are worn before you open the pump

Rietschle's fault table for the KTA /4 lists damaged blades as a cause of two symptoms: insufficient suction or pressure capacity, and abnormal noise. In practice, short vanes show up as:

• Lower vacuum or flow than the pump gave when new, with the inlet and exhaust filters clean and no leak in the pipework. Rule out the filters first: Rietschle lists obscured inlet or exhaust filters as the first cause of low capacity.
• A change in running noise. Rietschle lists damaged blades and a worn cylinder as the pump side causes of abnormal noise.
• More carbon dust in the built in filters between services. The dust is the vane material itself.
• Higher running temperature, although Rietschle also traces this to high ambient temperature, blocked cooling air or a dirty exhaust filter.

None of these replaces the caliper. The only reliable way to know how much life is left is to take the cover off and measure.

What shortens vane life

Becker states that vane life depends mostly on two factors: temperature and vacuum level. The other causes in the makers' manuals all come back to heat, dirt or the vanes not moving freely:

• Heat. Install the pump where it has free air flow and a reasonable ambient temperature, and blow the dust off the pump and motor. Becker recommends doing this every 2,000 hours alongside the bearing grease.
• Running harder than needed. Becker's advice is to run the pump at the lowest pressure or vacuum the job accepts. Busch fits a vacuum relief valve on current Seco pumps to keep air flowing through the pump and protect the vanes, set slightly above the vacuum the application needs.
• Frequent starts. Becker says more than 3 starts per hour reduces vane life. Rietschle caps the KTA /4 at 12 starts per hour for the KTA 40 to 80 and 10 for the KTA 100 and 140.
• Grease and dirt in the slots. Rietschle warns that grease reaching the pump chamber mixes with carbon dust into a paste that sticks the vanes in their slots. A vane stuck in its slot cannot follow the cylinder wall. Busch's rule is simple: the vanes must drop freely in the slots.
• Vanes fitted backwards. Becker notes that a vane installed with the bevel the wrong way touches the cylinder at only one point, which accelerates wear.
• Dirty intake air. Becker's schedule calls for the intake filter to be checked and cleaned every 40 to 200 hours, with a new element after four cleanings and at least once a year.

Replacing the vanes

All three makers say the same thing: change the complete set, never single vanes. A mix of new and worn vanes leaves the rotor out of balance and the worn ones still short.

• Clean before fitting. Blow out the housing and the rotor slots with compressed air. Becker's guide allows a Scotch Brite pad, brake cleaner and light 220 grit paper in the slots, with no machining.
• Check each new vane slides freely in its slot before you close the pump.
• Fit with the bevel matched to the cylinder bore and pointing in the direction of rotation.
• Inspect the cylinder. Becker says to check the end shield for heat damage or scoring. A scored cylinder or end plate wears new vanes quickly, and Rietschle treats a worn cylinder as a workshop repair.
• Clean or change the filters at the same time. The old vanes have left carbon dust through the pump and filters.

Ordering the right vane set

Three numbers identify a vane set: the pump model from its nameplate, the vane size as length x height x thickness, and the number of vanes. Measure the length and thickness from an old vane. Do not use the worn height. Take the height from the vane set listing for your model instead.

Count the vanes. The same vane often ships in different set sizes for different pumps. The 240 x 48 x 4 mm Becker vane comes as a set of 4 for the KDT and KVT 3.140, and as a set of 7, Becker 90133400007, for the DVT 3.140. Across our range, sets run from 4 to 10 vanes.

Browse every size in our vacuum pump vane sets, or search by your pump's part number on the compatibility page. If your pump is not listed, send the model and a vane measurement through request a quote and we will match it.

Frequently asked questions

Can I replace just the broken vane?
No. Becker, Rietschle and Busch all specify changing the complete set. A new vane next to worn ones leaves the rotor unbalanced and the pump still short of capacity.

Which way round do carbon vanes go?
The bevelled edge goes outward against the cylinder, with the bevel following the direction of rotation so it matches the curve of the bore. Fitted backwards, a vane touches the cylinder along one line and wears fast.

How long do carbon vanes last?
There is no single figure. Becker's first vane check falls at 3,000 hours and Rietschle's at 4,000 hours, but heat, vacuum level and starts per hour decide the real life. Measure at each check and work out your own wear rate.