Shaft d1 and seat bore d7
d1 is the diameter of the shaft the rotating unit sits on, d7 the bore in the gland that takes the stationary seat (H8 tolerance per AESSEAL). The table gives d7 only where two sources agree.
Reference tool — not a selection
Find the EN 12756 size of a mechanical seal before it goes in an RFQ.
Mechanical seal to EN 12756
Shaft, installation length, seat bore.
Enter the shaft diameter d1, as a number or as it reads in a marking. A measured installation length and seat bore are checked against the table row; without d1 they find the shaft diameter. The buttons under the drawing step to the neighbouring sizes. Below, an offered seal can be checked on d1 and l1K.
Examples:
Replacement check
On d1 and l1K alone: face materials, elastomer and version are checked separately.
All 130 engineering tools
Mechanical seals in centrifugal pumps for cooling water, fuel and oil are often made for the space set by EN 12756 (formerly DIN 24960): the shaft diameter d1, the installation length l1K and the seat bore d7. Enter the shaft diameter or a marking such as EN 12756 35 KU, and the tool gives the table row, draws the seal section to scale and writes an RFQ line. If the seal is already out, enter the measured seat bore and installation length, and the tool finds the shaft diameter they fit.
The standard fixes the space for a seal, not the seal itself: face materials, elastomer and version are given separately, and whether a given seal type follows the standard is for its maker to confirm.
How an EN 12756 size is read
Three sizes of one space.
Installation length l1K
From the back face of the stationary seat to the end of the rotating unit: the short K version. Several shaft sizes share one l1K, from 35 mm at d1 14 and 16 to 65 mm at d1 90 to 100.
K and N, and the materials
EN 12756 has a short K and a longer N installation length; the sources print l1N for one maker only, so it is not given here. Face and elastomer materials are read in the seal material code reader.
| Shaft d1, mm | Installation length l1K, mm | Seat bore d7, mm |
|---|---|---|
| 14 | 35 | — |
| 16 | 35 | 27 |
| 18 | 37.5 | 33 |
| 20 | 37.5 | 35 |
| 22 | 37.5 | 37 |
| 24 | 40 | 39 |
| 25 | 40 | 40 |
| 28 | 42.5 | 43 |
| 30 | 42.5 | 45 |
| 32 | 42.5 | 48 |
| 33 | 42.5 | 48 |
| 35 | 42.5 | 50 |
| 38 | 45 | 56 |
| 40 | 45 | 58 |
| 43 | 45 | 61 |
| 45 | 45 | 63 |
| 48 | 45 | 66 |
| 50 | 47.5 | 70 |
| 53 | 47.5 | 73 |
| 55 | 47.5 | 75 |
| 58 | 52.5 | — |
| 60 | 52.5 | 80 |
| 65 | 52.5 | 85 |
| 68 | 52.5 | 90 |
| 70 | 60 | 92 |
| 75 | 60 | 97 |
| 80 | 60 | 105 |
| 85 | 60 | 110 |
| 90 | 65 | 115 |
| 95 | 65 | 120 |
| 100 | 65 | 125 |
A dash in the d7 column for d1 14 and 58 mm: the sources do not agree on it. The longer installation length l1N is not given: the sources print it for one maker only. Sizes d1 10 and 12 mm are left out: only one source gives them. All sizes in millimetres.
Sources
Installation length l1K: Chesterton’s 491 DIN data sheet, John Crane’s Type 59U data sheet and AESSEAL’s DIN SAI and stationary seat brochure, with the same values in EagleBurgmann’s MG9 data sheet. Seat bore d7: Chesterton, AESSEAL and EagleBurgmann; the H8 tolerance: AESSEAL. The data sheets are cited for the EN 12756 sizes alone, not as a description of the seals themselves.
Before you send the request
Questions about mechanical seal sizes in an RFQ
What is the installation length l1K?
It is the length from the back face of the stationary seat to the end of the rotating unit on the shaft, in the short K version of EN 12756. It sets where the rotating unit sits against the seat, so a seal with a different l1K presses its faces together with a different spring force, or does not fit the space at all.
Why does EN 12756 matter for a replacement?
EN 12756 (formerly DIN 24960) fixes the space a seal takes: the shaft diameter d1, the installation length l1K and the seat bore d7. Seals and seats of different makers that follow it are made to fit the same cavity. Whether a given seal type follows it is for its maker to confirm.
How do I find d1 when the seal is out?
Measure the shaft where the rotating unit sat. If the shaft cannot be measured, measure the seat bore in the gland and the length from the back face of the seat to the end of the old unit, and enter both: the bore picks out the shaft size (32 and 33 mm share a 48 mm bore), and the length narrows it, since several sizes share one l1K.
What should the request include?
The shaft diameter d1, the installation length l1K and the seat bore d7, the face and elastomer materials or the material code from the old seal, the seal maker and type if known, the pump maker and type, the quantity, and photographs of the old seal and its seat.
Size found?
Send the line with a photograph of the seal.
A table row is a cross-check of the size, not a seal selection. Attach photographs of the old seal and its seat, and Vessel Core checks them before an offer goes back.
Buyer tools
