Technical guides for choosing flat gaskets, O-rings and sealing materials — by medium, face condition, temperature, pressure and approval scope. Pick a topic, search, or dive in.
Five focused areas. Pick what you need.
118 articles · updated weekly
What DVGW, WRAS, BAM and KTW approvals cover, where they apply and how to know which approval your installation requires.
A practical guide to choosing between cellulose and aramid fibre gaskets. Compare temperature, pressure, media, creep resistance and approval requirements.
When O-rings need back-up rings: pressure, clearance gap, extrusion risk, one-ring vs two-ring support and what they do not fix.
Technical reference for BLUESEAL ULTRA 350: aramid/NBR construction, service limits, gas and oxygen document scope, chemical checks and joint-selection limits.
Why boiler water-side connections may leak after service. Six conditions change when a joint is opened: face, residue, gasket and load.
Water-side boiler gasket guide: diagnose leaks, measure the gasket, check material and source replacements safely.
UK boiler gasket sizes from 3/8 to 1-1/2 inch BSP. Common dimensions, 3/4 inch variants and what to measure before ordering.
Heat exchanger connection leaks are often misread. Check gasket, HX body, water tracking, scale and face condition before replacing.
Heat exchanger problems in combi, system and conventional boilers: scaling, contamination, gasket locations and sourcing checks.
Boiler pressure dropping repeatedly? Four common causes: system leak, bleeding drop, expansion vessel issue and PRV discharge.
Boiler pressure too high? Six common causes: expansion vessel, filling loop, overfill, PRV issue, bleeding pattern and plate HX fault.
Bolt tightening sequence affects gasket compression. Learn why cross-pattern tightening in stages reduces flange distortion and leak risk.
Torque is not bolt load. Learn how friction, lubrication, bolt size, nut factor and gasket seating stress control torque for flat gaskets.
BSPP and BSPT fittings explained: how each joint seals, where flat gaskets and PTFE tape belong, and how to identify the connection before choosing a gasket.
BSP flat gasket sizes for 3/8 to 2-1/2 inch flat face unions: typical OD × ID ranges, what the thread size tells you, and what to measure before ordering.
BSP thread sizes explained: nominal size, thread OD, TPI, BSPP vs BSPT, and how to identify a fitting without confusing thread size with gasket size.
A used flat gasket can come out in one piece and still be finished. Field explanation of permanent thickness loss, creep relaxation, face imprint and why a new gasket is normally the correct repair.
A used O-ring can look perfect and still leak after reassembly. Field explanation of compression set, hot-water service and why replacement is the correct repair.
Compression set is the permanent deformation an elastomer retains after sustained compression. What it means, how it's tested, and what the datasheet numbers tell you.
The gasket is cheap. The real cost of a leak is labour, downtime, repeat diagnosis, secondary damage and loss of system reliability.
Find whether a dishwasher hose leak comes from the inlet mesh washer, flat washer, hose body, tap connection or appliance-side fitting.
A dishwasher that fills slowly may have a blocked inlet mesh washer. Check the inlet connection before assuming valve or control faults.
EPDM vs NBR — which rubber to specify and when. Water, weather and heat vs oil and fuel. A straight guide to choosing the right material and avoiding seal failure.
ePTFE can suit damaged faces and low bolt load. Compressed fibre can retain seating stress better. Choose by face, load, medium and temperature.
Identify the expansion-vessel connection geometry, measure the gasket or sealing interface and reassemble it without confusing the connection seal with a vessel or valve fault.
How to tell whether an expansion vessel leak comes from the flat gasket, threaded joint, Schrader valve or vessel body before replacing parts.
Boiler expansion vessel gasket reference: 3/8 and 1/2 inch BSP sizing, rotating feed pipes, seized fittings and replacement checks.
Rapid gas decompression can blister or crack O-rings from inside. Learn the failure pattern, risk factors and why compound-specific RGD data matters.
How residue, scoring, pitting and raised burrs on large BSP flat-face joints interrupt gasket seating, and what to inspect before fitting a new gasket.
Virgin PTFE offers broad chemical resistance but cold flows under load. Filled PTFE reduces creep but narrows compatibility. Choose by medium, load and face.
Diagnose boiler pressure that rises while cold after the filling loop is closed: verify isolation, distinguish a passing valve from an external connection leak and follow the appliance procedure.
How to identify whether a filling loop leak comes from the washer, O-ring, valve, thread or connection face.
Trace an external leak at a removable filling-loop connection and identify whether the joint uses a flat washer, O-ring, threaded seal or another fitting-specific interface.
How to assess a stuck fitting without twisting pipework, rounding flats, damaging threads or ruining the sealing face before the gasket is removed.
Flange misalignment compresses flat gaskets unevenly. Learn how angular offset, lateral offset and bolt force affect gasket seating stress and repeat leak risk.
Radial scratches, circumferential marks and corrosion pitting affect gasket sealing differently. How to decide whether the face can be re-gasketed.
A polished flange face can reduce gasket grip and contribute to leaks without visible damage. How to spot a too-smooth face condition.
Surface finish affects gasket grip. Why serrated finish works, typical Ra ranges, and when a flange face is too smooth or too rough.
A flat gasket joint that sealed reliably can leak right after maintenance. Six field-tested causes — face imprint, debris, bolt friction, reused gasket, wrong replacement, disturbed alignment — and a step-by-step reassembly checklist.
Non-parallel flange faces compress a flat gasket unevenly. Learn why torque alone rarely fixes geometry, how to read the gasket mark, and when alignment must be corrected.
Why 1.5 mm and 2 mm flat gaskets are not interchangeable at large BSP flat-face unions, and how recess depth controls the correct thickness.
Flat gaskets and O-rings seal different joint designs. Plain engineering guide with examples from taps, hoses, valves and fittings.
Warp is a geometry problem, not a surface texture problem. Straight-edge check, gasket compression signature, tolerance table, and the three options when re-gasketing will not hold. Field diagnosis.
Practical guide to flat gaskets: how they work, where they are used and how to choose material by temperature, pressure, medium and face condition.
Technical reference for FLEXSEAL PRO 350: compressibility, service limits, leak-rate context, documentation scope and joint-selection limits.
FLEXSEAL PRO 350 is listed for refrigeration and cooling. Verify refrigerant, oil, pressure, temperature and flange condition before use.
Food and beverage gasket selection by FDA and EC 1935/2004 documentation, material grade, media, CIP chemicals and market requirement.
Why mixed metals corrode in flanged joints, how galvanic corrosion can create leaks, and what isolation gaskets can and cannot reduce.
Garden hose quick connectors seal on small O-rings. Why outdoor exposure causes leaks, why EPDM is usually better suited, and how to check size.
Gasket blow-out follows loss of seating control. Learn the warning signs, common assembly causes, and ways to reduce blow-out risk.
Read the compression mark on a removed gasket: uniform, one-sided, partial, absent or displaced patterns and what they usually indicate.
How to separate load loss from chemical attack by reading compression marks, swelling, softening, embrittlement and time to failure.
Flange rotation can reduce gasket seating stress at the bore edge even when bolt torque looks correct. Learn the radial compression signature and when flange stiffness, not gasket grade, is the real limit.
Why a gasket leak returns at one bolt position: local bolt load loss, face damage, flange rotation, mid-arc stress drop and how to read the gasket mark.
Central heating gasket material — by temperature, pressure, medium and approvals. Cellulose for domestic duties; aramid for higher-pressure, gas or commercial systems.
Choose gasket material for drinking water fittings by jurisdiction, approval scope, temperature and pressure.
Thicker gaskets are not safer by default. Select thickness by face condition, pressure, bolt load, material behaviour and equipment data.
Identify flat gaskets, fibre washers, rubber seals and O-rings by joint geometry, material and replacement clues. They are not interchangeable.
Compressed air may contain oil carryover. Choose EPDM or NBR by the actual air contamination, temperature and connection position.
Heat pump gasket selection by glycol compatibility, vibration, thermal cycling, potable-water duty and connection position.
Solar thermal gasket selection by stagnation temperature, glycol compatibility, thermal cycling and collector connection position.
Graphite composite gasket for steam, oxygen-documented service, boilers, thermal cycling and high-temperature industrial applications.
General-purpose cellulose fibre gasket for heating, water, glycol and standard industrial duties on clean flat faces.
Practical gasket selection for boilers, pumps, manifolds, heat exchangers and underfloor heating systems, with material and temperature notes.
Bolt load can shift after first heat-up. Know the difference between controlled retorque, hot torquing and unsafe live tightening.
How to measure a flat gasket by outside diameter, inside diameter and thickness, with field checks to avoid common sizing errors.
How to measure an O-ring by inside diameter, outside diameter and cross-section, then check the groove and nearest standard size.
A gasket datasheet contains temperature ratings, pressure limits, compressibility, leak rate and approval codes.
Select HVAC and refrigeration gaskets by refrigerant, compressor oil, pressure side, thermal cycling, vibration and flange condition.
Peroxide-cured EPDM O-rings for hot water, outdoor fittings and HVAC where compression set and long-term elastic recovery matter.
Replaced the gasket and the joint still leaks? Check material, face condition, thickness, alignment, bolt load and true leak source.
Diagnose large BSP flat-face leaks by checking gasket size, thickness, face condition, seating load, leak timing and compression marks.
Five reasons a boiler joint area can still leak even when the replacement gasket itself is not defective: face contamination, pump shaft seal, PRV discharge, condensate and reuse of the old gasket.
How to check whether a fitting is left-hand threaded or simply seized before adding force, with safety limits for gas, pressure and unknown-service joints.
Marine gasket selection by seawater, salt air, vibration and class society requirements. DNV, ABS and material limits explained.
Match obsolete gaskets without an OEM part number by measuring the joint, checking service conditions and choosing a compatible material.
How to measure a missing large BSP flat gasket: confirm joint type, measure the recess OD, ID and depth, then cross-check the BSP size.
184-piece household seal kit with flat gaskets, O-rings, aerators and mesh washers for taps, shower hoses and appliance connections.
What NBR (nitrile) rubber is, where NBR O-rings are commonly used, and when EPDM, FKM or another material may be a better choice.
Before recommissioning a joint that leaks immediately after reassembly, check face cleanliness, dimensions, alignment, load, joint geometry, material duty and the true leak source.
Outdoor O-rings often crack because the rubber is wrong for weather exposure. How ozone attacks NBR, why EPDM performs better, and what to check.
O-ring extrusion and nibbling explained: how pressure, clearance gap, hardness and backup rings affect seal damage and risk reduction.
How groove depth, width, squeeze and gland fill determine whether a static O-ring face seal or radial seal holds pressure reliably.
Choose O-ring lubricant by elastomer: EPDM, NBR, FKM, silicone and neoprene compatibility, plus combinations that can cause swelling.
Compare NBR, EPDM, FKM, SBR, silicone and neoprene O-rings by medium, temperature and service. Includes peroxide-cured EPDM notes.
What 70 and 90 Shore A mean for O-rings, how hardness affects sealing, extrusion resistance and installation tolerance.
You replaced the O-ring and it still leaks. Check size, material, groove condition, squeeze and installation damage before blaming the seal.
Stretch and squeeze interact. Too much stretch thins the O-ring cross-section and can reduce effective squeeze in static sealing grooves.
Outdoor tap leaking at the hose connection? Check the flat washer inside the fitting, the tap face and the correct EPDM replacement size.
A joint that leaks does not need more torque — it needs diagnosis. Overtightening extrudes the gasket, crushes the bore edge and distorts soft fittings.
More force is not always the fix. Overtightening can crush flat gaskets, deform O-rings and damage soft fitting faces.
How brass, galvanised steel, copper, plastic and stainless fittings affect flat gasket choice through face condition, duty, temperature and approval requirements.
How to tell whether a dripping PRV is caused by valve seat failure, overpressure, a vessel fault, overfill or a connection washer.
PTFE has broad chemical resistance, but cold flow can reduce bolt load. How virgin, filled and expanded PTFE differ in gasket service.
PTFE tape seals tapered threads. Many BSP plumbing joints use parallel threads and seal on a flat gasket instead.
How to identify pump union gasket size from the old gasket or union recess, without confusing 15mm, 22mm and 28mm pipe size with gasket dimensions.
Why a pump union can still leak after a new gasket: scale, residue, wrong thickness, overtightening, face damage or pipework stress.
A practical diagnostic guide for pump union leaks: confirm the source, read the leak location, check the face, gasket and alignment before blaming the gasket.
Raised face and flat face flanges seal differently and need the correct gasket form. Mixing them can cause leaks or flange damage.
Rigid vulcanised cotton-cellulose gasket for documented water-service duties; selection depends on the exact listing, joint load, geometry and operating conditions.
How to remove old gasket residue without damaging the mating face, and what to check before fitting the replacement gasket.
RUBBERSEAL flat-gasket family with EPDM 80 Shore TBG sizes and SBR 70 Shore GGM sizes. Select by exact SKU, material, temperature and joint duty.
Saturated and superheated steam create different sealing conditions. Use continuous steam temperature, not peak rating alone, when selecting gaskets.
How to tell whether a stuck fitting is seized, cross-threaded or overtightened before applying more force and damaging the joint.
A shower hose leak often comes from the flat washer at the connection. How to find the leak point and replace the correct seal.
Static O-ring seals sit between stationary surfaces. Dynamic seals work with movement, friction and wear, so selection rules change.
Why flat gaskets can leak after the first steam heat cycle, how bolt load drops, and how to separate material limits from assembly faults.
The thread may be intact while the joint still leaks. How to check the sealing face, washer, gasket, seal type and joint geometry.
One spanner turns the fitting. The other holds the fixed side. When two spanners are needed and what can happen when the joint is unsupported.
Many washing machine hose leaks come from a failed flat gasket or mesh washer at the connection. How to identify the leak source safely.
How hydraulic shock can open a leak path in a gasketed joint that sealed under steady pressure, and what to check before replacing the gasket again.
Above 1 inch BSP, gasket area, face condition and tightening load matter more. How larger flat gasket joints become more sensitive to small errors.
A flat BSP union washer suits only the joint geometry designed for it. Recognise taper threads, O-ring grooves, cone seats, bonded seals and flange-gasket joints before selecting the seal.
When a softer gasket helps minor face damage, and when it only masks wrong sizing, low bolt load or the wrong joint type.
Where 11/4 to 2-1/2 inch BSP flat gaskets appear: plant rooms, commercial heating, buffer tanks, pump stations, valves and process skids.
The wrong tool can round fittings, twist pipework and damage joints. How to choose ring, open-ended, adjustable or pipe grips on site.
Why larger BSP gasket leaks in commercial and industrial systems cost more: access, isolation, fluid loss, downtime and repeat disassembly matter more than gasket price.
What sustained load, temperature, medium exposure and face contact change inside a used gasket — and why appearance alone cannot qualify it for reuse.
Tell us your temperature, pressure and media — we'll match the right gasket line in one reply. Or use the interactive selector and see the answer in real time.