35 mm shaft, 45 mm seal: the sleeve trap on a Gilkes 301-45 pump

35 mm shaft, 45 mm seal: the sleeve trap on a Gilkes 301-45 pump

A real job from October 2026. Customer name withheld.

If a pump seal leaks as soon as it's fitted, the first question isn't "which seal?". It's "where does the seal actually sit?". This job is a good example.

The problem

A customer needed a new mechanical seal for a Gilkes heavy-duty pump, part number 301-45, on a Cummins QSV engine. They had already bought a seal online. It leaked as soon as it was assembled. They came to us asking for a 35 mm replacement.

We asked questions before we quoted

A quote based on a part number alone is a guess. So before pricing anything, we asked for:

• the exact shaft size, and whether there is a step or a sleeve
• the stationary seat's inside diameter, outside diameter and thickness
• the liquid, its temperature and its pressure
• any markings on the old seal, and photos

The find: the shaft wears a sleeve

The customer measured it the same afternoon. The pump shaft is 35 mm, but a sleeve sits over it. The seal doesn't run on the shaft. It runs on the sleeve, and that is 45 mm.

Order by shaft size and you get a 35 mm seal: the wrong size for this pump.

The duty

• Liquid: fresh water (engine jacket water)
• Temperature: up to 90°C
• Pressure: 2 to 3 bar

The choice

We offered two options in a 45 mm elastomer bellows seal:

• Carbon / ceramic faces with nitrile rubber. Lower cost, and fine for cooler, gentler duties.
• Silicon carbide / silicon carbide faces with Viton rubber. Hard-wearing faces and heat-resistant rubber for hot water.

For fresh water at up to 90°C, we recommended option 2. The customer chose it.

The seal we supplied

• 45 mm elastomer bellows mechanical seal
• Silicon carbide / silicon carbide faces
• Viton elastomers
• Boot-mounted stationary seat

How fast

• Under 24 hours from first enquiry to a quote, with a datasheet and the size problem solved
• Next day from order to despatch, by Royal Mail Special Delivery

The lesson

Measure where the seal sits, not just the shaft. Sleeves, steps and worn shafts all change the size a seal needs. A two-minute check with a calliper saves a leaking pump and a wasted part.

Got a leaking seal? Send us a photo and a measurement, and we'll identify the right seal.

• Website: acumenseals.co.uk
• Email: office@acumenseals.co.uk
• Phone: +44 7767 842601

Andrew Sykes MCGI, Director, Acumen Seals & Pumps Limited.

Gilkes and Cummins names are used for identification only. No affiliation is implied.

FAQ

What size seal does a Gilkes 301-45 pump need?

It depends on whether the shaft has a sleeve. On this pump the shaft was 35 mm with a sleeve, so the seal ran on 45 mm. Always measure the diameter where the seal sits.

Why did my new pump seal leak straight away?

The most common cause is the wrong size or type for the shaft or sleeve. Other causes include a damaged seat, poor fitting or the wrong materials for the duty. Send us a photo and measurements and we'll check.

Which seal materials suit engine jacket water at 90°C?

For this duty we recommended silicon carbide faces with Viton elastomers. Carbon and ceramic faces with nitrile rubber suit cooler, gentler duties.

What should I measure before ordering a mechanical seal?

The shaft or sleeve diameter where the seal runs, the stationary seat's inside and outside diameters and thickness, the liquid, its temperature and its pressure. Photos of the old seal help too.