3/2 Coax Pneumatic Valve

3/2 way coax pneumatic valve range.

External air Namur mount pilot pneumatically actuated 3/2 way coaxial valves are supplied according to size, 3 way coax valve air operatedfunction, pressure, media and flow, and coax valve suppliers offers ranges of 3 port 2 position air driven coaxial valves to suit most applications, but the vast array of choice can sometimes lead to confusion. For example 3 way air operated coax valves are available with different port sizes from 1/4 through to 2" with various connections such as BSP- NPT - Flange PN16 PN40 PN100 PN200 etc, various orifice sizes offering different flow rates, a range of operating pressures, various materials of construction and a choice of elastomer and PTFE sealing options and valve functions to help provide the best cost effective solution to match the application at hand.

Below are example of the more popular 3/2 air actuated coaxial valves, all have options for normally closed or normally open. Stated maximum pressures shown are according to maximum inlet pressure however coaxial valve can handle back pressures at reduced rates typically 16 bar maximum.

You can view a typical technical data sheet here...

Basic Principle

How 3/2 coaxial pneumatic valves work.

Valve working basics.

3/2 way externally operated coax valve normally closed

3/2 normally closed coaxial pneumatic valve

Pressure: Flow P to R maximum

Flow A to P or R to P 16 Bar

3/2 way coaxial pneumatic valve normally closed

Fail safe Closed - Flow P to R, P to A closed

3/2 way coaxial pneumatic valve normally closed - actuated

Actuated Open, Flow P to A, A to R closed.

 

 3/2 way externally operated coax valve normally open

3/2 normally open coaxial pneumatic valve

Pressure:

Flow P to R maximum

Flow A to P or R to P 16 Bar

3/2 way coaxial pneumatic valve normally open

Fail safe Open - Flow P to A, P to R closed
 3/2 way coaxial pneumatic valve normally open - actuated
Actuated Open, Flow P to R, P to A closed.

Normally Closed Function

How a Coaxial 3/2 way normally closed pneumatic valve works.

symbol for 3/2 way normally closed

3/2 way normally closed pilot symbol

The coaxial valve is in the fail-safe closed state.

These externally controlled pneumatic valve is in the rest or fail safe position, with the control tube (2) through which the medium (blue) flows being pushed by a compressed spring (3) against the seal of the valve seat (1). The valve is thus permanently closed from the input P to output A. From P to output R, the medium can be flow through the valve.

3/2 way normally closed coax valve - closed position

The coaxial valve is in the energised open state.

By supplying the compressed control air at the port 4, the space in the cylinder is set under pressure, which pushes the control tube (2) in the axial direction away from the valves seat (1) and so releases the flow path passage from P to A. The opposite side of the control tube is at the same time pressed in the 3/2 Way valve seat (4) and so closes the passage from A to R. Due to this shift in the valve, the return spring (3) is compressed.

When port 4 is exhausted to atmosphere, the compression spring (3) pushes the control tube (2) back to its initial position in the valve seat. The valve is then closed from P to A. Connection from P to R is thus open again.

3/2 way normally closed coax valve - open position

Normally Open Function

How a Coaxial 3/2 way normally closed pneumatic valve works.

symbol for 3/2 way normally open3/2 way normally open pilot symbol

The coaxial valve is in the fail safe open state.

When the Normally open valve is in the rest position, the control tube (2) through which the medium (blue) flows, is pressed by a compression spring (3), to the left away from valve seal (1) and results in an open passage P to A and in turn pushes against 3/2 way seal $4) thus closes the connection from P to R.

If the valve is pilot operated by a 5/2 Way Pilot valve, the control tube is pressed away in addition to the spring, by means of control air (green) on port 2 from the valve. The space at port 4 is thus vented to atmosphere.

3/2 way normally open coax valve - open position

The coaxial valve is in the energised closed state.

If the space in the cylinder is filled through the port 4 with the control air (green compressed air), the control tube (2) moves in the axial direction away from the 3/2-Way valve seat (4), and so opens the passage from P to R. The opposite side of the control tube is pressed at the same time into the valve seat (1) and thus closes the passage from P to A. Due to this tube shift in the valve, the return spring is compressed further.

When venting port 4, the return spring (3) shifts the control tube (2) back to its initial position away from the 3/2 valve seat. The valve is then open again.

3/2 way normally open coax valve - closed position

Technical Data Sheets

Click on the links below for the full PDF technical data sheets.
ModelPressure (Bar)Port ThreadPort TypeOrifice Sizes (mm)Body MaterialSealing
380 64 1/4, 3/8, 1/2, 3/4, 1, 11/4, 11/2 and 2" BSP, NPT Thread or flange 10,15,20,25,32,40,50 Brass, AISI303 stainless steel, 316 Stainless steel or Brass nickel plated FKM,PTFE
381 100 1/4, 3/8, 1/2, 3/4, 1, 11/4, 11/2 and 2". BSP, NPT Thread or flange 10,15,20,25,32,40,50 Brass, AISI303 stainless steel, 316 Stainless steel or Brass nickel plated FKM,PTFE

3/2 Coaxial air valve orifice sizes and flow rates.

Coaxial pneumatically actuated valves are supplied with a wide choice of orifice sizes giving choice of various flow rate coefficients which can be allocated to various port connections. The orifice size is the internal media flow diameter of the coax valve internal laterally moving tube that controls the flow, so bigger diameter tubes offer higher flow rates, smaller tubes lower flow rates, but there are limitations. These limits relate the port size diameter should not be less than the internal tube diameter as the smallest flow path is the key flow restriction point, thus having a smaller port size and a larger tube and body would not give any increased flow. For example a 1/4 port with 10mm orifice will work correctly but the same 1/4" port with 6mm through put would not gain any additional flow if fitted with say a 20mm tube as the major flow obstacle is at the port ends of the coaxial valve. One bonus with various orifice to port sizes is that there can be several orifice or flow coefficient options for the same port size typically at the same price and manufacturers will not typically offer options that are not based on sound engineering practice.

Valve options

Media Temp: -10°C to +100°C Max

Ambient Temp: -10°C to +50°C Max

Switching time: 50 to 1000 ms

Mounting: any position

Sealing: FKM, optional NBR or EPDM

Body material: Brass (MO), 304 stainless steel (V2), 316 stainless steel (V4)

Special Options:

Nickel plating (02)

Vacuum version (12)

Mounting brackets (15)

Oil and grease free (16)

Normally closed (A), Normally Open (B)