Chapter 11 - Valves and Actuators with the NAMUR-interface
1. Pneumatic actuation of process valves
Process valves can be actuated manually, electrically, pneumatically and hydraulically. Often times pneumatic actuators are in use when it comes to automated process valves. They are mostly either linear actuators (pneumatic cylinders) or rotary actuators.
Further important elements can be:
The design and dimensions of rotary actuators differ from manufacturer to manufacturer. The two most popular designs are either Scotch-Yoke or Rack and Pinion actuators. We will introduce you to the Rack and Pinion actuator with more detail.
The selected size of the actuator depends on the force required to open and close the process valve. Usually the manufacturer indicates the maximum torque the actuator offers at a specific pressure.
There are two versions of linear actuators:
In double acting actuators - depending on the direction required - compressed air flows to the outside or to the inside of the two pistons. This can be easily controlled by using 5-way directional control valves (5/2-way for fully opening and closing the process valve, 5/3-way if intermediate positions are required).
There are standards for the contact interfaces of a rotary actuator, e.g.:
NAMUR-valves are control valves which offer an assemblage interface according to the standard VDI/VDE 3845.
NAMUR-valves are different from other in-line valves as they offer two ports on the flat side of the valve. In addition, there are holes for fixing the valve onto the actuator.
The drawing below shows a single solenoid 5/2-way valve with an interface according to NAMUR. The dimensions of the 1/4” -interface, among others, are shown as well.
A normal 3/2-way inline valve has 3 ports. The 3-way NAMUR-valve on the photo however has 4, which you can also see on its ISO symbol. WHY IS THAT?
That is why in process automation, we aim towards an air recirculation into the spring chamber, also called a “purge”.
By feeding process air into the spring chambers, we want to reduce pollution inside the actuator due to dirt, dust, mist, moisture etc. that might have been sucked into the spring chambers and thus avoid corrosion of the springs.
HAFNER Pneumatik offers a uniquely wide range of valves with NAMUR-interface, as well as a range of accessories.
HAFNER does not only offer standard products but also offers:
Standard sizes of HAFNER NAMUR-valves:
Series 701| orifice: 7 mm | flow: 1250 l/min | ports: G 1/4" – 1/4" NPT | NAMUR 1, 1/4"
Series 101| orifice: 10 mm | flow: 2250 l/min | ports: G 3/8" | NAMUR 1, 1/4" à maximized air-flow
Series 121| orifice: 12 mm | flow: 3000 l/min | ports: G 1/2" – 1/2" NPT | NAMUR 2, 1/2"
Conforming to standards, the flow measurement is shown as nominal flow in [l/min]. Nominal flow: at p1= 6 bar, p = 1 bar, stream-value of the compressed air (l/min).
Besides maximum flow of 1.250 l/min in a compact design there are 10 more competitive advantages of the Hafner NAMUR-valves series 701.
1. PA fixing nut, which protects the solenoid system from wetness and moisture.
2. Coil MA 22 fully covered with PA or Epoxy (on request), 360° rotatable. Others (Ex-versions) available on request.
3. Brass operator tube, including O-ring to protect solenoid system from wetness from the bottom.
4. Head made from PA.
5. Brass manual override for turning; other versions and materials (e.g. stainless steel) on request.
6. Spool made of stainless steel; other inner parts are: brass, POM, NBR, FKM.
7. Fixing screws, stainless steel.
8. Body, anodized aluminum.
9. End-cap made from brass.
10. Unique sealing system, the HAFNER swimming O-Ring.
MNH 350 701: HAFNER NAMUR-Flex valve
DRN…: Flow regulator plates
UB 701: NAMUR Air-recirculation block