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Frequently Asked Questions
How does a square section seal differently?
With a flat face against a flat surface rather than line contact.
That gives a broader contact area.
A round section contacts along a narrow band.
The broader face suits static sealing particularly.
Nothing moves across the seal in those applications.
That is where the profile is at its best.
Why is it more stable in the groove?
A square section cannot roll.
That makes it easier to fit correctly in deep or awkward grooves.
It removes the twisting problem round sections have during assembly.
A seal that stays where it is put matters on long installations.
Twisted o-rings are a common assembly fault.
The square profile largely eliminates it.
Does it resist extrusion better?
At pressure, yes - more material sits at the groove edge.
It resists being forced into the clearance gap.
A round section of the same nominal size extrudes more readily.
That is why square sections appear in higher-pressure static work.
They are also used as back-up rings behind o-rings.
Clearance gap and pressure together determine whether extrusion is a risk at all.
Is it suitable for dynamic sealing?
Generally not - the flat face generates more friction.
It does not accommodate movement or misalignment forgivingly.
Reciprocating and rotating duty suit round or lobed sections better.
O-rings and quad-rings are the usual answer there.
Wear on both seal and surface is higher with a flat contact.
Static applications are where the square profile earns its place.
Can it drop into an o-ring groove?
Not reliably - the groove has to suit the geometry.
A groove designed for a round section may give the wrong squeeze.
Too little squeeze leaks; too much accelerates wear.
Groove width and depth both matter.
Confirming rather than assuming interchangeability is necessary.
Manufacturers publish groove dimensions for each profile separately.
Machined or moulded?
They differ in tolerance, cost and available sizes.
Moulded rings suit volume and standard sizes.
Machined rings suit non-standard sizes and tighter tolerances.
Lead time on machined rings is generally longer.
Cost per unit is higher but tooling is avoided.
For one-off or repair work, machined rings frequently make sense.
How is the material chosen?
By fluid compatibility, temperature and pressure.
Fluid compatibility comes first.
Temperature range then narrows the compounds.
Pressure determines whether extrusion needs addressing.
Profile and compound are separate decisions.
Both have to be right for the seal to work, and getting one right does not rescue the other.