Type A vs Type B Drain Cock Valves – What's the Difference?
If you're replacing a drain cock valve or fitting a new plumbing or heating system, you've probably come across Type A and . While they look very similar, one key design difference determines where each should be used.
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 valve) provides a convenient point for draining water from a plumbing or central heating system.
They are commonly installed on:
- Central heating systems
- Domestic water pipework
- Commercial plumbing installations
- Compressed air systems
- Water storage systems
Drain cock valves make maintenance much easier by allowing water to be safely drained before repairs, servicing or system upgrades.
What Is a Type A Drain Cock Valve?
A Type A drain cock valve includes a gland seal around the spindle.
This gland prevents water escaping through the threads while the valve is open, making it the preferred choice where water could otherwise leak onto surrounding surfaces.
Benefits of Type A Drain Cock Valves
- Prevents water escaping around the spindle
- Cleaner draining process
- Ideal for indoor installations
- Reduces unwanted leaks
- Better suited to finished floors, cupboards and utility rooms
For most domestic plumbing and central heating systems installed inside a property, Type A is generally the recommended choice.
If you're replacing an existing valve indoors, browse our range of Type A Drain Cock Valves for a reliable replacement.
What Is a Type B Drain Cock Valve?
A Type B drain cock valve does not include a gland seal.
When opened, a small amount of water can escape down the valve threads before leaving through the outlet. This isn't usually a problem where drainage occurs outdoors or into an area where minor water loss isn't a concern.
Benefits of Type B Drain Cock Valves
- Simpler construction
- Cost-effective option
- Suitable for external pipework
- Ideal where small water loss isn't an issue
What's the Difference Between Type A and Type B Drain Cock Valves?
The main difference is that Type A valves have a gland seal, while Type B valves do not.
Because of this:
- Type A valves prevent water escaping around the spindle while draining.
- Type B valves may allow a small amount of water to run down the threads.
If your valve is fitted inside your home, garage or plant room, Type A is usually the better option as it helps prevent unwanted water dripping onto floors and surrounding surfaces.
If the valve is installed externally or where a little water loss isn't an issue, a Type B valve is often perfectly suitable.
Which Drain Cock Valve Should You Choose?
Choose a Type A Drain Cock Valve if:
- The valve is installed indoors.
- The system is above finished flooring.
- You want to minimise water leakage.
- You're working on a central heating system.
Choose a Type B Drain Cock Valve if:
- The valve is installed outside.
- Small water loss isn't a concern.
- You want a more economical option.
- The system drains into a suitable area.
What Colour Should the Water Be When Draining a Heating System?
While draining your heating system, the colour of the water can indicate the condition of the system.
Grey Water
A light grey colour is generally normal and expected.
Black Water
Very dark or black water often indicates a build-up of sludge and magnetite within the heating system.
Sludge can:
- Reduce radiator performance
- Create cold spots
- Increase boiler running costs
- Shorten the lifespan of your heating system
Before refilling your system, it's worth using our Plumbco Sludge & Flux Remover to help remove sludge and restore heating efficiency.
Brown or Orange Water
Rust-coloured water usually indicates corrosion within the system.
After flushing, protect your heating system with Plumbco Corrosion Inhibitor, specially formulated to protect steel, aluminium, copper, their alloys and other common heating system materials against future corrosion.
Frequently Asked Questions
Are drain cock valves universal?
No. Drain cock valves are available in several thread sizes and connection types. Always check the pipe size and thread before ordering.
Can a drain cock valve leak?
Yes. Older valves can leak due to worn washers, damaged threads or corrosion. Replacing the valve is often the quickest and most reliable solution.
Can I replace a drain cock valve without draining the system?
In most cases, no. The section of pipework should be isolated and drained before replacing the valve.
Can Type B drain cock valves be used indoors?
They can, but because water may escape down the threads during draining, Type A drain cock valves are generally recommended for indoor installations.
Shop Drain Cock Valves Online at Plumbco
Whether you're a professional plumber or tackling a DIY project, Plumbco stocks a range of quality drain cock valves, drain off valves and plumbing fittings at competitive prices.
Browse our range today for fast UK delivery, competitive prices and expert customer support if you're unsure which valve is right for your installation.
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