A maintenance supervisor at a pharmaceutical plant had to replace the gasket used on a 20‑inch tank manway he acted in the normal manner that an experienced technician would act: he measured the outside diameter of the old gasket with the help of a tape measure, ordered for a new gasket of the same size, and passed it to the fitter. However, the new gasket did not fit in the correct manner and was slightly too thick — such that without putting in a lot of pressure, it could not fit onto the manway cover.
This would have led to over-compressing the elastomer and having it leak into the product zone. The issue clearly did not lie in the nominal size but in the lack of examination of the thickness of the gasket, cross-sections, and compatibility with the groove with regards to the specification set by the manufacturer of the manway. The manway sizes refer to more than just the diameter because the right dimensions for sealing depend on a set of dimensions including the cross-section, envelope and materials used for the gasket as well as the surface finish. This is useful information for all members of maintenance teams, process engineers, or procurement managers who work in hygienic plants.
What a Manway Gasket Does and Why Its Size Matters
The manway gasket refers to the sealing component that exists between the manway lid (the cover) and the manway body (the aperture in the tank). After the lid has been closed and the clamps or screws secured tightly, the gasket flattens as it presses down into the minor imperfections on the surfaces of these two metal parts, hence establishing a leak-proof seal capable of averting loss of the product, contamination, or infiltration of air or cleaning detergents. There is a need for the gasket to be chemically compatible with both the product and the CIP substances that flow through the tank system during its operation. In hygienic industries like pharmaceuticals, food and beverages, it is required for the gasket to conform to FDA standards and to be both non-toxic and non-absorbent while also being capable of not causing the generation of any grooves for bacteria to live in. All of these aspects of the functioning of the gasket depend on its size which includes its outside and inside diameter, thickness, and the kind of the cross-section. The gasket must have the correct dimensions, otherwise the size or thickness will not fit or seal properly.
For a complete understanding of the broader category of hygienic sealing components and how they integrate into a sanitary process line, our article on what a sanitary fitting is covers the design principles that apply to gaskets, clamps, and every other connection in the system.
Standard Manway Gasket Sizes and Dimensions
Manway gasket sizes commonly used in hygienic processing correspond to the nominal bore of the manway opening, generally varying between 12 inches to 24 inches diameter, with some larger custom sizes for very big vessels. Table below outlines standard sizes, actual envelope dimensions and usual usages of manway gaskets. The dimensions correspond to standard manway frames developed by sanitary equipment manufacturers and are compatible with ASME BPE and 3‑A general requirements for sanitary vessels.
| Nominal Manway Size | Typical OD (Outside Diameter) | Typical ID (Inside Diameter) | Common Thickness | Typical Application |
|---|---|---|---|---|
| 12 inch (DN 300) | Approximately 14.0–15.0 inches | Approximately 12.0 inches | 0.25–0.50 inch (6.4–12.7 mm) | Small ingredient tanks, portable vessels, pilot plant equipment |
| 14 inch (DN 350) | Approximately 16.0–17.0 inches | Approximately 14.0 inches | 0.25–0.50 inch (6.4–12.7 mm) | Intermediate storage tanks, buffer tanks |
| 16 inch (DN 400) | Approximately 18.0–19.5 inches | Approximately 16.0 inches | 0.31–0.50 inch (7.9–12.7 mm) | Fermentation vessels, mixing tanks, dairy silos |
| 18 inch (DN 450) | Approximately 20.0–21.5 inches | Approximately 18.0 inches | 0.31–0.62 inch (7.9–15.9 mm) | Brewery tanks, pharmaceutical reactors, large storage vessels |
| 20 inch (DN 500) | Approximately 22.0–23.5 inches | Approximately 20.0 inches | 0.31–0.62 inch (7.9–15.9 mm) | Large fermentation tanks, dairy silos, processing vessels |
| 24 inch (DN 600) | Approximately 26.0–28.0 inches | Approximately 24.0 inches | 0.38–0.75 inch (9.5–19.1 mm) | Very large storage and processing tanks, bulk liquid terminals |
The dimensions mentioned in this context are standard for manway gaskets that are fitted in clamped or bolted covers. Oval and obround manways that are used in some European vessels have a different dimensional family, and the particular type of gasket should be matched to the specific manway type. Always make sure to check the drawing of the manway actual manufacturer before requesting a replacement gasket. A gasket which is "almost" the right size will either cause leaking or fail to allow the cover to seal correctly. Eagle Fittings produces replacement gaskets in standard sanitary sizes in EPDM, Viton (FKM), and PTFE with corresponding FDA-compliant material certificates.
Material Choices and Their Impact on Gasket Selection
The type of a manway gasket influences the gasket's temperature resistance, chemical compatibility, and the gasket's durability during repeated CIP and SIP cycles. The below table gives an overview of the three common elastomers and polymers used for hygienic manway gaskets, their applications, and associated costs.
| Material | Temperature Range (Continuous) | Best For | Relative Cost |
|---|---|---|---|
| EPDM (Ethylene Propylene Diene Monomer) | -30°C to 150°C | Hot water, steam, CIP solutions, most dairy and food applications. Excellent resistance to polar solvents and caustic cleaning chemicals. Not suitable for oils or hydrocarbon‑based products. | $ – Economical; the default choice for most hygienic applications. |
| Viton (FKM, Fluoroelastomer) | -20°C to 200°C | High‑temperature SIP cycles, aggressive chemical environments, applications involving oils, fats, or acidic products. Superior chemical resistance to EPDM. | $$ – More expensive than EPDM; used where the chemical or thermal environment exceeds EPDM's capabilities. |
| PTFE (Polytetrafluoroethylene) | -200°C to 260°C | Near‑universal chemical resistance. Used for the most aggressive chemical environments, for ultra‑high‑purity applications, and where even trace leaching from an elastomer is unacceptable. PTFE is less resilient than EPDM or Viton and may require a higher clamping force to achieve a seal. | $$$ – The most expensive option; reserved for extreme chemical or purity applications. |
Gasket Profile and Groove Compatibility
A manway gasket does not exist as a flat sheet instead it contains a specific profile of the cross-section which needs to match the profile of the groove present in the manway frame. Several profile types are used in the construction of hygienic manways. The commonest profiles are rectangular, D-shaped and O-ring gasket. The rectangular gasket lies inside a flat groove and seals by compressing elastomer surface fully against the cover. The D-shaped or O-ring gasket is placed inside a rounded groove and seals by deforming the surface in the right way so that its contact area is reduced.
These two types of gaskets are not interchangeable. If the D-shaped gasket is installed in a flat groove, an uneven sealing will result in a leak. It is necessary to double-check the manway gasket profile against the design provided by the manufacturer or against the old gasket if its reliability has been confirmed. If neither option is available, making a mould from the clay and comparing it against the profiles from the catalog provided by the supplier can be the right decision.
What Does a Replacement Manway Gasket Cost?
The size and material of a manway gasket along with its certification level affect its price. The price of 12-inch EPDM gaskets for hygienic manways varies from $40 to $80. The price of 20-inch Viton gaskets is in the range of $120 to $250. The manufacture of the 24-inch PTFE gasket is very costly and has a cost range of $250 to $500 or more. All of the prices mentioned are retail prices corresponding to individual purchases; however, the cost for large purchases and OEMs is much lower.
The price of the gasket is only a small part of the cost incurred due to the problem with the gasket. Making sure to keep a small number of backup gaskets in stock is reasonable because it will save lots of money in case of overheating of the manway gasket. GVC and CSI Designs provide more information on making use of manway gaskets as part of the sanitary sealing process.
Installation, Inspection, and Replacement Schedule
The manway gasket is known to wear out with time. Every time the manway is opened, the gasket is compressed and released. Every cycle of CIP or SIP causes the gasket to undergo thermal and chemical stress. Because of this constant compression, the elastomer will be deformed and unable to compress any more. Although a gasket that has been used for more than a year may appear undamaged, it will be ineffective when the manway cover is closed. The correct approach is to replace the manway gaskets according to a schedule, i.e. routinely, usually once a year, or according to the recommendations of the gasket manufacturer. However, if a gasket cannot be effectively replaced, it has to be visually examined for deformations and other types of damage.
Frequently Asked Questions
How do I measure my existing manway gasket to order a replacement?
It is necessary to determine the outer diameter (OD), inner diameter (ID), and thickness of the gasket. Make sure to identify the shape of the cross-section as rectangular, D-shaped, or O-ring. You can verify the measurements against a standard size table or share them with the gasket vendor. Try to use the dimensions listed in the manufacturer's drawing when selecting the appropriate size of the gasket.
Can I cut a manway gasket from a sheet of elastomer?
In case of a temporary repair that does not require critical pressure, it is possible to make a gasket out of any sheet material, although for hygienic applications it is not a good idea. A cut gasket would have a flat surface without any specific profile, as well as no exact compressibility properties like the ones of a moulded gasket. Furthermore, it's practically impossible for a cut gasket to fulfill all of the required surface finishes and certification requirements.
Why did my new manway gasket fail after only a few months?
Chemical incompatibility is one of the major reasons of premature gasket failure i.e. a gasket material is not suitable for the product or for the chemicals in the CIP procedure; it can be caused by the overcompression of the elastomer which causes it to extrude and deform; and it can also result from the effect of heat when SIP processes are performed above the gasket material’s temperature limit. In order to prevent gasket problems, ensure that the gasket material matches both the chemical and thermal environment, and that the lid is closed according to the manufacturer’s instructions and is not over-tightened.
How do I know if I need an EPDM, Viton, or PTFE manway gasket?
Select the material according to the strictest chemical and thermal conditions the gasket will encounter. For routine dairy and food applications using hot cleaning-in-place (CIP) procedures, EPDM is the standard material. For high-temperature steam-in-place (SIP), oils, or aggressive acids, Viton is the necessary material. In cases of severe chemicals or ultra-pure applications where there can't be any leaching of elastomers, PTFE is the right choice. The gasket supplier may also provide chemical compatibility charts to validate the material choice.
References
- Alfa Laval — Hygienic Manway and Tank Components. Manufacturer of hygienic manway covers, frames, and sealing systems, with dimensional specifications and gasket selection guidance.
- GVC — Sanitary Gaskets and Sealing Solutions. Supplier of hygienic gaskets, including manway gaskets in EPDM, Viton, and PTFE, with dimensional data and chemical compatibility resources.
- CSI Designs — Sanitary Gasket Selection and Installation. Distributor and technical resource for hygienic gaskets, clamps, and fittings, with guidance on gasket sizing and material selection.
- 3‑A Sanitary Standards — Gasket and Seal Standards. The hygienic equipment standard that defines material, design, and cleanability requirements for gaskets used in dairy and food processing.
A manway gasket is a simple component with a demanding job: it must seal a large‑diameter opening against pressure, temperature, and chemical attack, cycle after cycle, while presenting a crevice‑free surface to the product. Getting the size right — the diameter, the thickness, and the cross‑section — is the foundation of that performance. A gasket that matches the manway frame, the groove profile, and the chemical environment will seal reliably for its full service life. One that is "close enough" will eventually leak, and the cost of that leak will always exceed the cost of the correct gasket. Eagle Fittings supplies replacement manway gaskets in the standard hygienic sizes and materials, with the FDA‑conformant certifications and the dimensional accuracy that a regulated process demands.
