Terminology
Quick Release connectors or couplings (QRC’s) as they are widely known are designed to provide a fast connection without the use of tools in circumstances where the connection and disconnection of lines need to made quickly, smoothly and repetitively. One half is usually attached to a flexible line.
QRC’s are made up of two mating parts. These are a female half and a male half. The female half is referred to as either the ‘Socket’ or the ‘Coupler’ or ‘Coupler Body’, and the male half is called either the ‘Plug’ or the ‘Nipple’ or ‘Nipple Body’.
Valve Configurations
QRC’s come in three main valve configurations; each one with different flow characteristics. The options are single shut-off, double shut-off and straight thru (full flow) connections. Each of these referrers to the type of valve incorporated within the design of the fitting. Each design has a different impact on the control of the media flow, flow rate and pressure drop or Delta P.
Straight-thru / Unvalved / Full Flow 
Double Shut-Off 
Single Shut-Off
Double Shut Off QRC’s are most commonly used in hydraulic applications and are sometimes referred to as ‘hydraulic couplings’. They feature a shut-off valve in both the female coupler and the male nipple connection, allowing the user control at both ends of the line. This means that virtually no fluid is lost on connection or disconnection. These quick release couplings can be used for either air or fluid transfer. You have to be aware that if you disconnect with residual pressure in either of the lines, you will experience hydraulic lock on reconnection if none of the residual pressure is released.
The reason it is called a single shut-off QRC is that a shut-off valve is found in the female socket but not in the male probe; only one half of the system is valved. The female half should be installed on the upstream supply of the line. This way it is possible to shut-off the media supply when the quick coupling system is disconnected.
If there is a shut-off valve already in place in the line assembly, it is possible to use a straight-thru or Unvalved configuration, since the QRC does not need this inbuilt element of control. Unvalved QRC’s offer a range of benefits. Since there is no valve mechanism on either part of the quick coupling, the flow is totally unrestricted resulting in superior flow rates, and also means there is very little pressure drop.
Where Are QRC’s Used?
QRC’s can be used for applications across all industries. These can include Pharmaceutical/Life Sciences, Nuclear, Automotice, Rail, Military, Aerospace, Oil and Gas, Construction, Food Processing, Transportation and Renewable Energies. QRC’s are utilized in fuel systems, cooling, test rigs, air tools and irrigation. They work well in confined spaces and the connection sits inline with the hose and pipe works.
How Do QRC’s Work?
QRC’s are a simple push-to-connect coupling. QRC’s can be locked together with a ball bearing mechanism, with the male half locking into the female socket once the sleeve of the female coupler is pulled back. Some QRC’s do not require the sleeve to be pulled back and can be classed as an automatic ocnnection. QRC’s can also be locked together using a bayonet mechanism or clasps. Each type of locking mechanism has its advantages depending on the application and size of connector. They are easy to operate and no tools are required.
Which QRC Should I Choose?
In order to select the right QRC, you must consider the following factors:
- Pressure
- Flow
- Temperature
- Functional and Environmental Considerations
- Media
- Maximum Allowable Pressure Drop Across All the System (Delta P)
Pressure & pressure surges
This is one of the most key elements for consideration. QRC’s cannot be used if the system pressure is greater than the rating of the fitting. All QRC’s are pressure rated according to the operating pressure, as well as burst pressure. This should be checked ahead of purchase. The pressure must be taken into consideration on connection and disconnection. As residual and pump pressures will have very different impacts on the system design and product selection. Pressure differential is also another factor to consider. If the pressure on the supply QRC when connecting is far greater than the connecting receiving QRC, you can experience high velocity across the QRC valve which COULD eject the seal from the valve and create system failure.
Flow
Flow rates are what dictates the size of the QRC. This can be affected too by valve configurations.
Temperature
This is particularly relevant to the seals and the compatibility of materials. The temperature of the media will also affect the material of the fitting and which metal you’ll need to use. For more information on chemical compatibility and seal materials please consult one of our experienced sales engineers.
Function & environment
Considerations such as corrosion, maintenance and cleanliness also play an important role in selecting the right system. Operating conditions, such as how easy the fittings are to access, the forces required to connect and disconnect, how much media loss you can tolerate, air inclusion, vacuum, weight, and size are all major considerations.
How Is Pressure Drop Calculated Through A Valve?
The pressure drop across a valve is related to the flow rate passing through it, i.e. the greater the flow rate the higher the pressure drop and the lower the flow rate the lower the pressure drop.
Manufacturers publish a Flow Coefficient value to allow the calculation of pressure drop based on flow rate.
For metric units, i.e. m3/hour and bar or l/s and kPa, the flow coefficient is Kv, whereas, for imperial units, i.e. gpm and PSI, it is Cv.
A l/s and kPa are most commonly used, we will concentrate on Kv and not Cv.
The formula for calculating pressure drop is:
Δp = (36Q/Kv)²
Where:
Δp = pressure drop (kPa)
Q = flow rate (l/s)
Kv = flow coefficient (no units)