Large diameter O rings, made to fit the groove and the duty
Author: Andrew Sykes MCGI
How do I source a large diameter O ring without mould costs or minimum orders?
Some large diameter O rings can be made without a dedicated mould for each size. Some manufacturing routes also allow small quantities. But no mould charge and no minimum order are not universal promises. They need confirming against the size, cross section, compound and manufacturing method.
The first question is not how cheaply the ring can be made. It is how the ring needs to seal.
Diameters and sections
Available diameters, cross sections and compounds depend on the route and the supplier, and must be confirmed at quotation.
Mould charges
Some manufacturing routes avoid a dedicated mould for each size. Any tooling charge must be confirmed at quotation.
Minimum quantities
Some manufacturing routes allow small quantities. Any minimum quantity must be confirmed at quotation.
When the catalogue does not cover the size
A vessel lid or filter housing may need a diameter that is not a stock item. A dedicated mould can make a small replacement order expensive. A minimum order can leave the plant buying more rings than it needs.
There are alternatives to commissioning a complete new mould. These include continuous moulding processes and rings made from cord with a vulcanised joint. They are different manufacturing routes. They should not be treated as interchangeable because both produce a complete ring.
Ask how the ring is made
Ask whether the proposed ring is continuously moulded or joined from cord. If it has a joint, ask how that joint is made and what duty it is suitable for. A glued joint is not the same as a hot vulcanised joint.
Some joined cord products are specified for static sealing only. Do not assume suitability for a moving seal, pressure cycling or vacuum service. Ask for confirmation against the actual application.
No size limit is not a specification
The available diameter depends on the process and the supplier. So do the available cross sections, compounds and tolerances. There is no single diameter at which every catalogue stops.
Confirm the required inside diameter and cross section together. Ask what tolerance can be supplied and how the finished ring will be inspected. A large ring still needs controlled dimensions.
Do not copy a tired dimension
A used O ring may have stretched, swollen, flattened or shrunk in service. Its measured size may not be the original design size.
Start with the drawing or original part specification where available. Check the groove dimensions and the condition of the removed ring. If the drawing has gone missing, use the sample as evidence rather than treating it as the specification.
The material still has to suit the duty
Record the product, cleaning chemicals and any steam cycle. Include the temperature, pressure, vacuum conditions and whether the seal is static or moving. Specify the compound and hardness, not just the rubber family.
For product contact duty, request the relevant declaration and traceability for the exact compound. The size of the ring does not remove the need for material evidence.
Deciding between FFKM and FKM? Read the FFKM vs FKM comparison or the FFKM chemical compatibility chart.
What should I send for a quotation?
Send the drawing or groove dimensions. Give the required inside diameter, cross section, tolerance and quantity. Include the compound, hardness and complete operating duty. State any inspection, traceability or product contact requirements.
Ask the quotation to confirm the manufacturing route, any tooling charge, minimum quantity and lead time. Do not assume that terms offered for one ring apply to every size or material.
Independent specification support
I am Andrew Sykes MCGI, an independent sealing specialist with 36 years in sealing. I look at the application before the supply route.
If you have a large diameter O ring with an old sample but no clear specification, send the drawing or the information you have. The aim is a ring that fits the groove and the duty, not simply a ring that can be made.
Telephone: 07767 842601
Email: office@acumenseals.co.uk
Acumen supplies large O rings selected for the groove and duty. Moulded and joined cord routes are checked against your application.Large O rings supplied for your application
Large O-rings, questions answered
What is the largest O-ring diameter available?
There is no single diameter at which every catalogue stops. Some manufacturing routes can make very large rings, but the available diameter depends on the process and the supplier. Tooling charges, minimum quantities, available diameters, cross sections and compounds depend on the manufacturing route and the supplier, and must be confirmed at quotation.
Is there a mould cost on a large diameter O-ring?
Sometimes, depending on the route and supplier, so always confirm it in the quote. Some manufacturing routes avoid a dedicated mould for each size, but that is not a universal promise.
What is the minimum cross section?
It depends on the manufacturing route, the supplier and the compound. Confirm the required inside diameter and cross section together at quotation.
What cross sections are available?
The available cross sections depend on the process and the supplier. Tooling charges, minimum quantities, available diameters, cross sections and compounds depend on the manufacturing route and the supplier, and must be confirmed at quotation.
Which materials are available?
Available compounds depend on the route and the supplier. Specify the compound and hardness, not just the rubber family, and for product contact duty request the relevant declaration and traceability for the exact compound.
What tolerances apply?
Ask what tolerance can be supplied for the proposed route and compound, and have it stated on the quotation. A large ring still needs controlled dimensions.
How are large O-rings inspected?
Ask how the finished ring will be inspected, and agree it before the order is placed. Inspection options depend on the supplier.
How are they packed and delivered?
Packing, labelling and lead time depend on the supplier and should be confirmed in the quotation. Do not assume that terms offered for one ring apply to every size or material.
Related reading
Send your large O-ring sizes
Internal diameter and cross section, or the groove dimensions, and we will quote the correct large O-ring in the right material.
Send the sizes, get a straight answer
Internal diameter and cross section, or the groove dimensions, and we will quote the correct large O-ring.
Andrew Sykes MCGI, 36 Years in Sealing