Washer and O ring buying guide

High-quality washers for watertight seals

Whether you're working at home, in the car or in an agricultural or industrial environment, it's advisable to have all the information on the type of liquid you're hoping to seal before you set about choosing a washer or O ring.

With all brands racing to make profits, there are a lot of cheap washers in the shops. If the material and characteristics of the washer aren't clearly stated, it's best to look elsewhere. Choose a leading supplier and you can rest easy knowing your connections are safe no matter if they are subject to pressure or not.

Replacing a washer: the basics

With the exception of plumbing washers, which are fairly easy to select, you will have to consider the following factors if you have to replace washers or O rings in another other type of installation:

• connection type;

1. dynamic;

2. static;

• type:

1. liquid or gas type (natural gas, water, etc.)

2. flat washer;

3. O ring;

4. tap washer;

• material:

1. fibre;

2. rubber;

3. copper

• dimensions:

1. internal diameter (ID);

2. outer diameter (OD);

3. thickness.

Washers and O rings come in a range of materials (aluminium, copper, and so on) and in various shapes (lobed, cup, etc.).

Washers can be split into two broad application categories: static and dynamic. All new appliances and pipework are fitted with washers and these parts are only replaced as part of regular maintenance or when leaks occur.

1. Static washers are used for stationary connections and are designed to be compressed.

2. Dynamic washers, on the other hand, are designed to withstand repeated movements (e.g. for taps, and hydraulic and mechanical applications).

The following types of washers and O rings are commonly used in residential water supply and heating systems.

1. Vulcanised fibre washers

2. EDPM rubber washers

3. Tap washers

4. O rings (also used for dynamic applications)

Fibre washers should technically be referred to as fibre gaskets. However, the term 'washer' is commonly used. Up until a few decades ago, these washers were made using asbestos and had to be entirely redesigned. Some old appliances may still be sealed with this highly resistant material and it's important to deal with the matter quickly as possible.

Vulcanised fibre washers: how do they work?

Most pipe gaskets are made of vulcanised fibre. The process of vulcanisation involves adding sulphur to a base material as it is heated to make the molecules more elastic. This process provides the material with the mechanical properties required and also works to make the material less prone to deformation.

Fibre washers or gaskets are used for fixed connections in plumbing and heating systems. It is recommended to measure internal (ID) and outer diameters (OD) carefully to ensure the connection does not fail or leak.

Before fitting a fibre washer, make sure that the two sides of the join are clean and well aligned and that they won't cause any abnormal traction.

Fibre washer materials and uses

EDPM (ethylene propylene diene monomer) is a type of synthetic rubber. EDPM rubber washers can be used to seal any connection that doesn't require a high compression set.

They are used in PVC pipes, water softeners, pool filters, domestic traps (sinks, showers, etc.), toilet flushes, washing machines and garden hose connectors. These washers simply need to be set in place by hand.

Do not use these washers for any metal assemblies that require tools for tightening and beware: these washers can slip out and end up in your pipes which will lead to blockages!

Common rubber and fibre washer sizes

Washers can be measured in imperial or metric units. The most common imperial sizes for residential applications include 3/8, 1.2, 3/4 inch and 1 inch. Common metric sizes include M4, M5, M6, M8, M10, M12, M16 and M20 (measuring the outer diameter).

By far, the easiest way to ensure you buy the right size of washer is to simply measure the washer you are replacing using vernier or digital callipers.

O rings can be used for static seals (e.g. taps) or for dynamic applications (e.g. pistons). These torus-shaped rings may also be called toric joints.

The standard DIN / ISO 1629 governs the classification and designations of these seals. The most common and widely sold O rings are made of NBR (Nitrile).

The hardness of these seals is measured in shores with three categories available:

• 70 shores

• 80 shores

• 90 shores

They are used to seal fixed hydraulic and pneumatic components.

O ring sizes

In order to choose the correct O ring you need to take three measurements: Outer Diameter (OD), Internal Diameter (ID) and Cross Section (CS). All measurements should be taken in millimetres using a vernier or digital calliper.

Using an O ring for dynamic applications

Nitrile O rings can also be used to create dynamic seals within the following reasonable limits:

• short-stroke rotation or translation: translation: 12 m/min; rotation : 6 m/min;

• maximum speed: max. 60 cycles/min.

For tougher applications, you will need more resistant materials (see table below).

These O rings are heat-resistant and compatible with petroleum and silicone fluids. They are commonly used to contain hydraulic fluids as well as non-aromatic fluids and solvents.

Common O ring uses

• Piston seals (dynamic): designed to slot into a cylinder groove as the piston slides in the cylinder, these O rings deal have to withstand radial compression.

• Static sealing applications as flange or cover seals compressed by a solid pad.

The O ring must match the size of the groove perfectly. O rings may be designed in line with metric (mm) or imperial (inch) size standards.

To make the right choice you need to think about the internal diameter of the groove and width. If there is no groove, lay the O ring flat, check it is round and measure the inner and outer diameter using vernier callipers.

O ring applications

Please note: a back-up ring, or anti-extrusion ring, must be used for support in high pressure applications. This ring is used in conjunction with the O ring allowing it to extend the operating pressure of the O ring. There are several different types of back-up ring including solid, spiral wound, and split. These rings can be made from elastomer, PTFE and many other materials.

As the name suggests, these washers are designed to seal compression taps. They may be solid or feature holes depending on the type of tap. These washers are made up of one or more layers of EPDM.

They can be used for both hot and cold sanitary applications. The maximum temperature they can withstand is 110°C.

This type of washer is often altered as the tap is turned repeatedly. Over time, a circular mark will impress into the washer and the polymer will start to break down. At this point, the washer will need to be replaced to avoid leaks.

To pick the right size, simply measure the diameter and thickness of the washer and check if it features holes or not.

Washers and gaskets designed to seal gas connections need to be chosen with care.

Each packet of washers must provide the following information:

• Standard

• Reference number

• Type (application and size)

• Compliance with standards

• Size

• Quantity

• Use before date

• Batch number

• Tightening torque required

• Temperature range: 20°C to + 60°C

Flat washers for gas applications are UV-resistant and non-slip.

Who hasn't used a few profanities after seeing oil dripping out of a driveshaft or the engine of a chainsaw or strimmer...? Lip seals are designed to seal in oil and are able to withstand fast and repeated rotations. Only a lip seal is able to seal a moving part against a stationary supporting surface (i.e. housing or casing).

Something of a technological marvel, these seals are made up of:

• an elastomer structure;

• a metal case;

• one or two sealing lips;

• a torus-shaped spring (optional).

The whole lip seal is lodged into a housing around which a shaft or transmission will turn. These washers are designed to prevent any drop of lubricant from passing through and must be replaced in case of leaks.

If you are replacing the washer yourself, you will have to measure the:

• internal diameter (around the shaft);

• outer diameter (where the seal is inserted);

• thickness.

In addition to these dimensions you will also have to check whether you need one or two lips. Choose the correct material bearing in mind that elastomer sub-categories include:

• NBR (Nitrile Buna Rubber)

• KFM (fluorocarbon-based fluoroelastomer)

Some lips feature grooves designed to push lubricant back towards the inside. Don't forget to look out for this detail.

Special tools are required to fit and remove these washers. Make sure you have the right equipment when fitting or removing a lip seal.

It's a good idea to have a stash of one or several sets of washers and O rings to deal with unexpected leaks. However, bear in mind that these materials will break down over the years.

Considering the low price of these parts, it's best to stock up on washers and O rings for every type of connection around you.

Don't forget to write the date of purchase on the packets and keep the seals away from chemicals, dust and sources of heat.