Both products are sold as "PTFE" manlid seals, but the PTFE sits in a different place in each. In a PTFE braided seal, the PTFE is the sealing body—fibers are braided and compacted into the joint. In a Super Tank Seal, PTFE is only the outer skin: an EPDM elastic core carries the compression while a three-side virgin PTFE encapsulation handles media contact. Compression mechanism, groove fit and recovery behavior all follow from that structural difference, so the two products cannot be treated as interchangeable on the basis of material name alone.

• Similar PTFE materials do not mean identical sealing performance.
• Compression behavior and groove compatibility are the decisive selection factors.
• Any replacement requires verification of dimensions, media and operating conditions.

 

Understanding the two manlid seal structures

What is a PTFE braided manlid seal?

A PTFE braided seal is a continuous rope braided from PTFE fibers into a square or round cross-section. The braid architecture—not the raw polymer—decides how it behaves: interlaced fibers create voids that let the rope deform and spread against the sealing surface, and braid tension controls how much of that deformation is recovered when load is released. Many products also carry an impregnation (silicone oil, graphite) that fills part of those voids.

Two consequences follow: the rope must be compressed enough for fibers to close surface micro-gaps, with no separate elastic element pushing back, and it must be cut to exact developed length and joined correctly—a bad seam is not recoverable with bolt torque.

 

What is a Super Tank Seal?

A Super Tank Seal is a composite: a round EPDM core provides elasticity, and a virgin PTFE film is wrapped over three sides, leaving the base open. The encapsulation is positioned so it carries media contact rather than compressive stress—the core takes the load and returns it as contact pressure.

The PTFE skin protects the core from most cargo and cleaning chemicals but is not a complete barrier. The EPDM core still defines the chemical envelope: mineral oils, some organic solvents and ozone remain outside its range, and permeation through the encapsulation seams brings media directly to the core. Both must be checked against the actual content.

 

How do their sealing mechanisms differ?

Compression and sealing contact

A braided seal reaches tightness through fiber deformation. As the manlid closes, the rope compacts and the fiber mass spreads laterally to fill irregularities in the sealing surface. Contact pressure comes from the compacted fiber body itself, so the compression is effectively fixed by how far the manlid travels.

A Super Tank Seal reaches tightness through core deflection. The EPDM core acts as a spring: it compresses under load, pushes back across the circumference, and keeps pressing after the manlid stops moving. A braided rope therefore needs a defined compression window, while an encapsulated seal needs a groove that stops the core extruding sideways.

Elastic recovery after compression

Recovery is the ability of a compressed seal to push back after the load is released, or after the lid has been opened and closed several times. It matters because a manlid seal is not a one-time joint—it is opened for cleaning, inspection and cargo changes.

A braided PTFE structure has limited recovery: once compacted, the rope does not return to its original cross-section, and each cycle removes a little more available compression. An encapsulated structure separates the functions—PTFE skin as barrier, EPDM core as spring. Recovery is still not unlimited: the core takes compression set, and what remains depends on core geometry, temperature history and storage—but it becomes a designed property rather than a by-product of fiber packing.

 

 

 

Sensitivity to installation conditions

Four variables decide whether either structure will seal:

• Groove geometry—depth, width, and whether the groove is semi-circular or flat rectangular. A round encapsulated profile needs groove constraint; a braided rope needs a surface it can spread against.
• Compression amount—too little leaves contact pressure below media pressure; too much crushes the structure and destroys its recovery.
• Bolt loading distribution—uneven torque produces a seal that is tight on one arc and slack on the other, whatever the material.
• Sealing surface condition—scratches, corrosion pits and residue from the previous gasket create leak paths no seal can bridge.

No retention-rate, compression-percentage or service-life figures are quoted here for either structure; those values are product- and application-specific and must come from the verified specification of the seal under consideration.^[1]

 

PTFE braided seal vs. Super Tank Seal: key differences

 

Comparison factor	PTFE braided seal	Super Tank Seal
Structure	PTFE braided fibers	EPDM core with 3-side virgin PTFE encapsulation
Sealing mechanism	Fiber compression and deformation	Elastic core compression and recovery
Elastic support	Depends on braid construction	Provided by the EPDM core
Compression behavior	Depends on braid and impregnation	Depends on core geometry and material
Installation	Requires suitable compression	Requires suitable groove and compression
Chemical compatibility	PTFE fibers and impregnant	PTFE surface and EPDM core
Temperature	Verify product-specific rating	-25°C to +110°C
Maximum pressure	Verify product-specific rating	4 bar

 

Three rows carry the purchasing decision. Elastic support and recovery is the clearest divide: a braided rope is a compacted fiber mass with no separate spring, while an encapsulated seal is a designed spring under a barrier—so ask for the core's compression-set data, not the PTFE's chemical resistance. Installation and compression ask two different questions: whether the groove gives a braided rope the right compression window, and whether it holds a core in place. Chemical compatibility ends where the word "PTFE" ends: the impregnant is the braided seal's weak link, the EPDM core is the encapsulated seal's.

 

How to choose based on actual service conditions

Chemical compatibility

Check four media separately: cargo, cleaning chemical, its concentration, and any residue left between loads. For a braided seal, confirm the impregnant against all four. For a Super Tank Seal, confirm both the PTFE skin and the EPDM core, and treat long contact or elevated temperature as a reason to verify permeation rather than assume encapsulation is absolute.

Temperature, pressure and vacuum

Establish normal, maximum and minimum temperature, operating pressure, pressure peaks, and whether the tank is ever pulled under vacuum during cleaning or discharge. The Super Tank Seal is specified at -25°C to +110°C with a maximum of 4 bar.^[1] These are ratings for the complete seal, not for the PTFE film or the EPDM compound alone. For a braided seal, obtain the supplier's verified rating for the exact product—do not transfer raw PTFE's temperature capability to a rope with an impregnant inside it.

Groove geometry and compression

Record groove depth, width, gasket cross-section, resulting compression and bolt torque sequence. Depth plus cross-section should give a compression the seal is designed for. A seal that is dimensionally correct but lands outside its compression window will leak—the most common cause of a "correct size, still leaking" complaint.

Opening frequency and maintenance

Count manlid openings per month, cleaning frequency, maintenance intervals and previous leakage records. Frequent opening puts a premium on recovery; a lid held closed for months is a different problem. Leakage records also separate progressive failure from an immediate selection or installation error.

Quick selection matrix

 

Service condition	What should be evaluated?
Aggressive chemicals	PTFE surface, EPDM core or impregnant compatibility
Frequent opening	Elastic recovery and compression behavior
High pressure	Verified pressure rating and groove design
Temperature fluctuations	Core material stability and compression recovery
Repeated leakage	Groove condition, dimensions and installation

 

The matrix deliberately names no winner for any row. In practice the deciding factor is usually the groove you already have and the cargo you actually carry—not a general ranking of materials.

 

Can you replace one seal structure with another?

Four risks of direct replacement

1. Different compression mechanisms.The groove was dimensioned for how the original seal compresses; a substitute that compresses differently sits at the wrong load.
2. Mismatched cross-section and compression amount.Nominal size can match while compressed height does not—which is how a seal "fits" and still leaks.
3. Incompatible groove geometry.A round encapsulated profile in a flat rectangular groove has nothing to constrain it; a braided rope in a semi-circular groove cannot spread correctly.
4. Different chemical compatibility limits.The failure point moves from impregnant to EPDM core or the reverse, so the media check must be redone, not inherited.

Five checks before replacing a manlid seal

 

Check	Information required
Existing seal	Photos, ID, OD and cross-section
Groove	Depth, width and sealing surface condition
Media	Cargo and cleaning chemicals
Operating conditions	Temperature, pressure and vacuum
Replacement reason	Leakage, wear or routine maintenance

 

When should you consider a custom seal?

Custom work is worth discussing when standard sizes do not match the groove, when the original gasket has leaked repeatedly despite correct installation, when service conditions have changed since the tank was specified, or when a different structure is being considered for an existing groove. It is not automatically the answer to a leak—but it is the right route when the catalogue does not contain the geometry you need.

Information needed for customization

1. Existing gasket photos and dimensions.
2. Groove drawings or measurements.
3. Cargo and cleaning media.
4. Temperature and pressure range.
5. Existing seal structure and the reason for replacement.

SUNPASS supplies Super Tank Seal and PTFE braided manlid seal options, and reviews groove and media data before recommending a structure. These five items are normally enough to start that review.

 

Common causes of manlid seal leakage

 

Leakage cause	What to inspect
Incorrect dimensions	ID, OD and cross-section
Insufficient compression	Groove and installation fit
Excessive compression	Seal deformation and compression damage
Uneven bolt loading	Bolt tightening and load distribution
Chemical incompatibility	Cargo and cleaning media
Damaged sealing surface	Scratches, corrosion and surface defects

 

Leakage is not automatically a material problem. Rule out these six mechanical and chemical causes first—several persist even with a perfectly matched seal.

 

FAQ

 

Can PTFE braided seals and Super Tank Seals be used interchangeably?
Not without verification. They differ in structure, compression mechanism and groove match. Before substituting, compare the seal cross-section against the groove profile, confirm the compression amount, and re-check media compatibility for the new structure—including the impregnant in a braided seal and the EPDM core in an encapsulated seal.^[2]

What is the difference between PTFE braided seals and PTFE encapsulated seals?
A braided seal is a fiber rope in which PTFE is the sealing body. An encapsulated seal is a composite in which an elastomer core provides elasticity and a PTFE film provides the media-facing surface. The first seals by fiber compaction, the second by core deflection.

Does a PTFE encapsulated manlid seal offer better elastic recovery?
The EPDM core is designed to provide elastic support, the mechanism a braided rope lacks. Actual recovery still depends on core geometry, temperature history and storage, so compare against the specific product data and the specific service cycle.

Is Super Tank Seal suitable for all chemicals?
No. The PTFE skin covers most cargo and cleaning chemicals, but the EPDM core sets the real limit, and seam permeation exposes the core directly. Verify both skin and core against the cargo, cleaning chemical and its concentration.

What are the temperature and pressure limits of Super Tank Seal?
The verified specification is -25°C to +110°C and a maximum of 4 bar.^[1] Confirm these against your cargo temperature, pressure peaks and vacuum conditions before specifying.

How do I choose the correct manlid seal size for an ISO tank container?
Measure the existing gasket's ID, OD and cross-section, and measure groove depth and width rather than relying on nominal tank size. Photos of the removed gasket and the groove, plus the tank designation, are the fastest way to avoid a size mismatch.^[2]