In many liquid chromatography applications, there is a need to limit the fluid flow to one direction. Check valves are the perfect solution for this need. There are several versions of check valves available, including standard check valves, non-metallic check valves, and even some specialized luer-based check valves. These valves are commonly used in Waters systems and Agilent systems.
The HPLC check valve directs the flow in one direction. These valves are usually ball and seat valves, and consist of a ruby ball and a sapphire seat. Ruby and sapphire are both crystalline forms of alumina oxide known for hardness, inertness, and the ability to be machined into durable components. An alternative to this type of valve is an electromagnetic valve called a solenoid seat.
When there is flow towards the ball, this flow exerts an upward pressure from the seat towards the base of the ball. When this pressure exceeds the pressure from the spring, the ball is forced away from the seat. Stopping the flow momentarily pushes the ball again the seat, thereby blocking the exit point on the HPLC check valve.
It is common for water–acetonitrile mobile phases cause ruby-sapphire inlet check valves to stick shut, often due to surface tension. Some scientists have concluded that the machined surface of the crystalline sapphire presents alumina oxide bonding sites which are activated in the presence of water, presenting a surface that was favorable for the seeding of aliphatic amines. This can be salved by using ceramic check valves, which are usually more expensive.
If your HPLC system has no or low pressure, this could be an indication that your check valve is faulty and should be replaced.
1. To begin cleaning your check valve on your HPLC pump, begin by disassembling the pump head and removing the valves with a spanner.
2. Sonicate them by 10% of nitric acid for an hour, and then rinse with HPLC grade water for a few minutes.
3. Reassemble the check valves
Check out our other valve articles, such as our most recent one on Rheodyne Valves!