Diaphragm Valve-KDV-Series
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Diaphragm Valve - KDV-Series
Features 
- Electropolished 316SS wetted parts construction
- 3 year guarantee
- Standard configuration: 300 psi at 200 °C
- No dead volume effect
- Positive port shut off
- Purging/sealing grooves design
- Adjustable commutation time
- Possibility of valve defect detection if installed in a K4000ng
- Elgiloy® diaphragm system
- Constant port pressure drop vacuum operation
- Allow new chromatographic method
- Also available for liquid media at higher operation pressure. See KDVL series brochure
Existing Valve on the Market
Since the introduction of the first G.C. 6 port diaphragm valves, more than 40 years ago (see pat# 3,140,615 filled oct.25 1962 by A.B. Broerman) up to today's recent G.C. diaphragm valve, the sealing concept didn't evolve at all (see fig#1).
The flow path is controlled by closing or blocking the fluid passage between valve's ports. This concept requires tight tolerances on plunger's length since any variation in their length will cause leaks.
This is also the reason why there is a wide difference in pressure drop from port to port. Since there is always some difference in plunger's length, it is extremely difficult to get proper sealing.
Many times, when a plunger is forced against the diaphragm to block the fluid flow between two adjacent ports, there will be a "cold flow" around it. This means that the fluid bypasses the plunger-defined area. This can be easily observed when increasing sample pressure; sample fluid can be detected in carrier circuit. Figure 1a presents the existing valve on the market.
Figures 1b to 1d presents the flow paths possible with this valve and illustrate the leaks.
The shortcomings from this design are:
- crossport leaks
- high pressure drop on selected adjacent ports
- does not work with vacuum sample
- dead volume appears when ports are closed
- limited functional pressure range
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New Chromatographic Method
This unique design allow for 2 new gas chromatographic method, like:
- Sample loop pressurization before injection (3-step sample injection) eliminating flow and pressure surge upon injection.
- Peak slicing, allow easy heart cutting and individual peak concentration, increasing at least by two the system sensitivity.
For example, application like the measurement of O2 and H2 become very easy. Ask for application bulletin, for KDV valve series application.
The peak slicing method is also covered by an international (PCT) patent pending.
See also product brochure and application bulletin for our new rotary g.c. valve design.
Product specification and design may change without notice. 
Contrôle Analytique's valve port system and purge/sealing groove system is so flexible that it can be used in many configurations. All these configurations could be actuated by an independently actuated plunger on each port.
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KDV-66 Port Selection Valve
This configuration could be used for direct replacement of existing old type diaphragm valves. Typical sample injection like shown in fig. 5 and fig. 6 could be realized.
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KDV-44 Port Selection Valve
This 4 port configuration allows many switching flow paths, and this with no dead volume effect.
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KDV-SSample Stream Selection Valve
Each port being independently actuated, sample stream flow path scheme or multiple column switching could be easily done. The sealing/purging groove prevents any inboard/outboard contamination and allows the possibility of issuing a proper alarm in case of leak.
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Valve system
Since it is clear that previous design was an important limiting factor in system performance of today's analytical equipments, we are now using the following valve design in our analytical system.
The system is based on an elementary 3-way switching cell, the KDV-3. The KDV-3 3-way cell can be seen in various positions in figures 2a to 2d, and is illustrated in figure 2e.
For switching from sampling to sample injection, the valve's ports are directly closed as shown in figure 3a and 3b. In our valve, the plunger is pushing on a Elgiloy® and polymer sandwich diaphragm.
The action of the plunger presses the diaphragm on the port's sealing surface to close it. The port's sealing surfaces are drilled in a surface just a few mils below the top surface. The sealing of the port has been tested with a ppb gas leak detector, and no leak could be detected even after the equivalent of 5 years of actuation at a pressure of 500 psig. This creates a positive tight shut-off valve.
The small displacement needed to close or open the port gives the valve a very short actuation time. A circular groove is machined around all ports to give a constantly swept circuit even if the port is closed.
This simple 3-way elementary switching cell could be used as a stand-alone 3-way valve, or multiple combination of it could be used to realize the function of a 6 port (or more) G.C. valve. There is no dead volume effect in this valve because of the unique flow path scheme. Actuated ports have positive tight shut-off, allowing high working pressure without any leak. All standard chromatographic configurations can be realized.
Many 3-way cells could be embedded in the same substrate (see figure #4). When doing so, extra purging/sealing grooves are added on the substrate. The purging/sealing grooves separate each switching cell.
These purging/sealing grooves can be swept by a clean carrier to eliminate the possibility of any inboard or outboard contamination and cross-port leak. The purge outlet could also be monitored to report any leak or to give the status of the valve's wear.
All those characteristics will give a long lifetime trouble free valve, and make system intelligent.
The valve shown in figure #4 is a 6-port diaphragm valve. This valve is actuated by two independent concentric actuators. This actuator is designed to give a full control of the switching time. These actuators are compact and compressed air actuated.
Contrôle Analytique's R&D team is working to make each plunger of the 6-port valve independently actuated. It will give the user a very flexible valve for many configurations.
This valve configuration is now used in the K4000NG trace gas analyzer system. This is the first time that a chromatographic system allows to diagnose and warn the user in case of valve malfunction. |
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