For the purposes of this guide we will use the following terms for the two halves of a quick release coupling:
The coupling and plug must be from the same series to connected together and each have three options: a female thread, a male thread or a hose tail (or barb).
Single/Double Shut Off
‘Single Shut Off’ means the downstream side (plug side) is vented to atmosphere when the coupling and plug are separated. Normal for compressed air couplings.
‘Double Shut Off’ means both sides (coupling & plug) are sealed when the coupling and plug are separated. Normal for hydraulic couplings.
When a single shut off coupling and plug are separated the air on the downstream side is vented to atmosphere. This release of energy can make the hose whip and cause injury. To avoid this ‘safety’ couplings should be used. Most new installations are now fitted with safety couplings as standard. There are many different types of safety coupling but almost all work by making the disconnection a two stage process. The first stage exhausts the air on the downstream side. The second stage allows the coupling and plug to be separated. The coupling and plug cannot be separated until the air has been exhausted.
How do you identify a coupling?
If there is no part number on the coupling half, compare the profile of the plug to a picture or a shadow chart. Some plugs have a distinct profile and are easy to identify but others look similar and are more difficult.
What type of coupling should you use?
The correct coupling for you depends on a number of factors including:
- What type is already in service in your factory?
- What flow rate do you require?
The most commonly used couplings are: