PTFE Balls — Frequently Asked Questions
The questions that come up most often when specifying PTFE check balls, valve balls and float balls.
What decides whether a check ball seals?
Sphericity, not diameter. A ball that is the right size but out of round will leak, because the seat contacts it on a high spot and there is a gap everywhere else. When specifying, state the sphericity requirement explicitly rather than assuming a diameter tolerance covers it.
Solid or hollow?
Solid for check and valve duty, where the ball must resist seating load and pressure. Hollow for float duty, where buoyancy is the requirement and the ball is not loaded. A hollow ball under seating pressure will collapse.
Which grade for a check valve?
Virgin PTFE is the default and suits most chemical service. Move away from it when the duty demands: carbon-filled for steam and hot condensate, glass-filled where creep at the seating band is the problem. Avoid bronze-filled in anything wet or chemically aggressive — the filler corrodes.
Why did my new ball fail faster than the old one?
Usually because the seat was not replaced. In a check valve the ball and seat wear as a pair, and fitting a new ball against a worn seat concentrates load on the damaged area. If a replacement ball fails quickly, inspect the seat before changing grade.
How does ball weight affect cracking pressure?
Directly, in a vertical check valve where the ball’s own weight must be lifted by the flow. Weight scales with the cube of diameter, so a small size increase changes cracking pressure significantly — and a change from virgin to bronze-filled nearly doubles the weight at the same diameter. Recheck valve behaviour after any grade substitution.
What size range is practical?
PTFE balls are made across a wide range, from a few millimetres up to several hundred. Very large balls are moulded rather than fully machined, and very small ones are usually machined. Diameter, tolerance and sphericity together determine which route is used.
Can PTFE balls be used in drinking water?
The resin can be suitable where it is FDA-listed for food contact, and unfilled PTFE is the grade to specify. Confirm the requirement that applies in your jurisdiction, and state it on the enquiry so the correct resin and documentation are used.
What should I send with an enquiry?
Diameter and tolerance, sphericity requirement, grade or the duty that will determine it, quantity, and — if it is a valve ball — the seat bore and cracking pressure.
Related pages
Weights by diameter are tabulated on the PTFE ball weight chart, and tolerance grades on the ball size and tolerance grade chart. For duty-specific selection see PTFE ball for check valve, for steam service and for cryogenic service. Send your requirement to HEMSUN.