Valve technology has come a long way with many available features. Gas and liquid multimedia valves that are used in chemical analysis such as Gas Chromatography/Mass Spectrometry (GC-MS) and Liquid Chromatography/Mass Spectrometry (LC-MS), two analytical techniques, are used for chemical analysis and have very critical requirements. In this blog, we will discuss key aspects to look for when replacing a solenoid valve, and possible upgrades to increase reliability and efficiency.
In chemical analysis, samples are separated using chromatography and identified with the mass spectrometer. Gas and liquid multimedia valves are used for head pressure control, flow path selection, and calibration in these analytical systems. These instruments can call for critical leak rates in the parts per fractions of a cc/min range; these are critical leak rates that require very high-end valves.
All valves are not created equal. When selecting a valve for analytical systems one must do his or her research. If you base your valve selection for your equipment on the lowest price, you'll likely experience equipment failures due to high leak rates over the valve's life and low repeatability. Analytical systems require valves that can withstand fast response time, high flow and repeated operations while maintaining precision control to ensure highly precise and accurate test results. The valves should be compared on leak rates, reliability, types of materials used and subsystem availability.
Leak rate is one of the most critical specifications for a valve used in Gas/Liquid (GC-LC) Chromatography, and Mass Spectrometry (MS). Instruments that leak can introduce outside contaminants into the sample flow stream and negatively affect the analysis. This means product failure. The original valve specifications must match to ensure it can withstand the necessary pressure and temperatures in the existing system. Valves used in GC, LC and MS should be tested using a helium mass spectrometer to check for porosity and permeability of the seat and seal. Other features that need to be considered are maximum pressure capability, surface finish, power consumption, and seat and seal.
- Pressure will directly affect the leak rate. The higher the system pressure, the higher the potential leak rate — higher-pressure rating means better leak rate.
- Surface finishes are essential in guaranteeing a low leak rate. Elastomers have specific leak capabilities due to material porosity/void fraction and permeation.
- Ability to be analytically cleaned. The analytical cleaning process is essential to ensure the valves don't introduce background or any contamination into the sample stream.
- Seat and seal load are determined by the system forces and sealing surface quality.
- Coil power consumption or coil force determines the spring force and pressure that can be applied to the valve. Valves with the same total power consumption can have different leak rates due to design, maximum designed pressure capability, orifice size, and magnetic materials.
Reliability and repeatability
When selecting valves in Gas or Liquid Chromatography and Mass Spectrometry (MS), reliability and repeatability are of utmost importance. For a valve to have repeatability it needs a long-life cycle, high yield rates, and a proven track record. When determining reliability in a valve you must evaluate the design, quality of material and manufacturing process and controls of the product.
Hit and hold
In high duty cycle applications, multimedia solenoid valves can generate heat at full voltage. In order to reduce this heat, higher-end valve manufacturers use Hit and Hold circuits. Hit and Hold circuits allow valves to be fully powered and remain in that state for a short time before voltage and current are reduced to lower levels, while still allowing the valve to remain energized. This procedure allows the valve to stay open with much less energy. This will also allow the valve to generate much less heat and decrease the power draw. As an OEM look for this type of circuit option in a valve to reduce heat, increase cycle life and reduce energy consumption.
Type of material is crucial for valves with critical leak requirements. The term wetted material is important to understand. The wetted material is defined as any surfaces and/or components that are (potentially) exposed to or in direct contact with the medium under pressure. A few more important things to know before selecting a valve are permeation rate, compatibility with certain fluids (specifically what your system uses), and potential out-gassing that can occur.
Finally, look for the availability of subsystems. A subsystem is a pre-assembled module that includes tubing, fittings, regulators, valves on a manifold and other accessories. A subsystem will eliminate the need to maintain multiple vendors and reduce the overall bill of materials, provide integration between components, create one single stream for technical support and customer service, and cost reduction in assembly and labor time.
Above is a Mass Spectrometry system that features two Parker subsystems. The backfill subsystem and calibration subsystem are examples of Parker's ability to provide customers with complete solutions. In these subsystems, Parker’s Series 9 and Series 4 valves were specifically selected because they offer:
- Non-corroding passivated stainless steel
- Ultra-low leak rate tested at 1 x 10 -7 cc/sec/atm Helium
- Pressure up to 1250 PSI
- High-temperature capability in a small size
- Easy implementation of Hit and Hold circuits
- Operation with extreme repeatability.
All valves can be customized with several attributes and come in complete pre-assembled subsystems to reduce time and cost. Parker is proud to be the only company capable of offering a complete product selection with integrating manufactured components and custom assemblies. We are eager to help you with all your precision gas and fluidics needs.
Parker Precision Fluidics has over 30 years of experience in developing valve and pump technologies. Our engineers specialize in helping Original Equipment Manufacturers (OEM) to update original valves that are producing low yields.
Our applications engineering team is always available to provide recommendations and customize equipment to customer specifications.
To learn more, visit Parker Hannifin’s Precision Fluidics Division or call 603-595-1500 to speak with an engineer.
Article contributed by Jonathan DeSousa, division application engineer, Precision Fluidics Division, Parker Hannifin.