If you're replacing a drain cock valve or fitting a new plumbing or heating system, you may come across Type A and Type B drain cock valves. While they look very similar, there is one key design difference that determines where each type is best suited.
In this guide, we'll explain the difference between Type A and Type B drain cock valves, when to use each one and how to choose the right option for your plumbing or heating system.
What Is a Drain Cock Valve?
A drain cock valve, also known as a drain off valve, drain valve or MT cock, provides a convenient point for draining water from a plumbing or central heating system.
Drain cock valves are commonly used on:
- Central heating systems
- Domestic water pipework
- Commercial plumbing installations
- Water storage systems
- Other systems where controlled draining is required
They make maintenance and repairs much easier by providing a dedicated point for safely draining water before servicing, replacing components or carrying out system upgrades.
What Is a Type A Drain Cock Valve?
A Type A drain cock valve features a gland seal around the spindle. This helps prevent water from escaping around the spindle and valve threads while the valve is open.
Because of this design, Type A drain cocks are particularly useful for installations where unwanted water dripping onto surrounding surfaces could be a problem.
Benefits of Type A Drain Cock Valves
- Gland seal helps prevent water escaping around the spindle
- Cleaner draining process
- Well suited to indoor installations
- Helps minimise unwanted dripping
- Suitable for areas such as finished floors, cupboards and utility rooms
For many domestic plumbing and central heating installations, Type A is a practical choice where the drain cock is located inside the property.
If you're replacing an existing valve, browse our range of Type A drain cock valves in a range of sizes and configurations.
What Is a Type B Drain Cock Valve?
A Type B drain cock valve does not have a gland seal around the spindle.
When the valve is opened, a small amount of water may escape down the valve threads before draining through the outlet. This makes Type B drain cocks better suited to situations where minor water loss around the spindle is not a concern.
Benefits of Type B Drain Cock Valves
- Simple construction
- Cost-effective option
- Suitable for external pipework
- Useful where minor water loss is not an issue
- Available in a range of sizes for different installations
Type B drain cocks can be suitable for external installations or other locations where any small amount of water escaping around the spindle will not cause a problem.
What's the Difference Between Type A and Type B Drain Cock Valves?
The main difference is the gland seal.
Type A drain cock valves have a gland seal, which helps prevent water escaping around the spindle when the valve is opened.
Type B drain cock valves do not have a gland seal, so a small amount of water may run down the threads while the valve is being used.
In simple terms:
- Type A: gland-sealed and generally better suited to indoor installations.
- Type B: no gland seal and suitable where minor water loss is not a concern.
If a drain cock is installed inside your home, garage, utility room or plant room, a Type A valve can help minimise unwanted water dripping onto floors and surrounding surfaces.
For external installations or locations with suitable drainage, a Type B valve may be perfectly suitable.
Which Drain Cock Valve Should You Choose?
Choose a Type A drain cock valve if:
- The valve is installed indoors.
- It is positioned above finished flooring or other surfaces you want to keep dry.
- You want to minimise water escaping around the spindle.
- You're working on a domestic plumbing or central heating system.
Choose a Type B drain cock valve if:
- The valve is installed externally.
- Minor water loss around the spindle isn't a concern.
- The valve drains into a suitable area.
- You're looking for a straightforward and economical option.
Always check the size, connection and application before ordering a replacement drain cock valve.
What Colour Should the Water Be When Draining a Heating System?
The colour of water drained from a central heating system can sometimes give you an indication of the condition of the system.
Grey Water
Light grey or slightly cloudy water can be normal, particularly on an older heating system.
Black Water
Very dark or black water can indicate a build-up of sludge and magnetite within the heating system.
Sludge can contribute to:
- Poor radiator performance
- Cold spots on radiators
- Reduced heating efficiency
- Increased strain on system components
If you're draining a heating system and find heavily contaminated water, it may be worth cleaning the system before refilling it. You can browse our range of heating system cleaners and sludge removers.
Brown or Orange Water
Brown, orange or rust-coloured water can indicate corrosion within the heating system.
After cleaning or flushing the system, a suitable inhibitor can help protect against further corrosion. Browse our range of central heating inhibitors and water treatment products.
Frequently Asked Questions
Are drain cock valves universal?
No. Drain cock valves are available in different sizes, connection types and configurations. Always check the pipe size and connection before ordering a replacement.
Can a drain cock valve leak?
Yes. Older drain cock valves can develop leaks due to worn washers, damaged seals, corrosion or deterioration of the valve itself. Replacing a worn valve is often the simplest solution.
Can I replace a drain cock valve without draining the system?
Usually, the relevant section of pipework needs to be isolated and drained before replacing the valve. The exact procedure will depend on the system and where the drain cock is installed.
Can Type B drain cock valves be used indoors?
They can be, but because Type B valves do not have a gland seal, water may escape around the spindle and run down the threads when the valve is opened. For indoor installations where this could cause a problem, a Type A drain cock is generally more suitable.
Shop Drain Cock Valves Online at Plumbco
Whether you're a professional plumber, heating engineer or carrying out a DIY repair, Plumbco stocks a range of drain cock valves, drain off valves and plumbing fittings.
Choose from different sizes and Type A and Type B options to find the right valve for your installation.
Browse the range online for competitive prices and fast UK delivery, or contact Plumbco if you're unsure which drain cock is suitable for your application.
