Dispensing valve for adhesives and assembly fluids

01

Pick the valve type for the fluid

Nordson EFD describes its 741V needle valve as applying low- to medium-viscosity assembly fluids with accurate, close repeat deposits: pulsed air acts on a piston to withdraw the needle a preset distance from its seat, and because the stainless steel needle shuts off at the dispense tip adapter there is virtually no dead fluid volume. Spring-loaded PTFE needle packings compensate for wear; fluid input is up to 300 psi (20.7 bar), actuating air 70–90 psi (4.8–6.2 bar), and the cycle rate exceeds 400 per minute. [1]

Fisnar's VD520-SS diaphragm valve instead separates the wetted parts from the moving parts with an inert UHMW-PE diaphragm, which its manual says suits reagents, paints, UV adhesives and other volatile substances. It is rated for 1–60,000 cps fluids, fluid pressure up to 70 psi (4.8 bar), operating air of 70–100 psi, up to 500 cycles per minute and a maximum flow of 60 ml/s of water at 70 psi; it is normally closed, opened by air on the piston and closed by a spring. [2]

Editorial note: the two valves differ in what touches the fluid and how much fluid pressure they accept. Ask the supplier which design they recommend for your fluid's viscosity, cure mechanism (moisture, UV, anaerobic) and filler content, and for a test on your actual fluid.

Give the supplier the fluid name and data sheet (viscosity, filler, cure type, pot life), deposit type and size (dot, bead, fill), tolerance, cycle time and dots per part, substrate and tip access, feed method (syringe, cartridge, pressure tank, pump), available air pressure and controller or robot interface.

02

Control the deposit and the cycle rate

Fisnar's manual states that the amount dispensed depends on valve open time, fluid viscosity, fluid pressure, diaphragm stroke and tip size, and that flow is fine-tuned with a stroke adjustment knob calibrated against a zero reference mark. [2] Nordson EFD's 741V likewise has adjustable fluid flow control by needle stroke and is used with its ValveMate 8000 controllers, a fluid reservoir and a disposable dispense tip. [1]

Editorial calculation: a part needing 8 dots in a 2-second cycle requires 8 / 2 × 60 = 240 valve cycles per minute, inside the 741V's quoted rate of more than 400 per minute and the VD520-SS's 500 per minute; at 400 cycles per minute each full open-close cycle has 60 / 400 = 0.15 s. Dot count and cycle time are assumed examples; robot travel between dots can set the real limit, so ask for a timed trial. [1] [2]

Because deposit size depends on fluid viscosity and pressure as well as valve settings, keep feed pressure and fluid viscosity stable and re-check deposits after changing fluid batches or tips. [2]

03

Consider a piezo jetting valve for small, fast dots

Axxon/Mycronic's APJ1500 piezo jetting valve data sheet describes non-contact jetting with no Z-axis motion, at up to 1,000 dots per second, which it states is 3 to 7 times faster than traditional jetting technologies, with a minimum dot of 0.14 mm and a minimum droplet of 1 nL. It lists underfill, dam and fill, hot melt, pin encapsulation, precision coating and corner or edge bonding as applications. [3]

The data sheet also lists temperature control of the valve body and fluid channel and a quick-release design for maintenance. Compared with the time-pressure needle and diaphragm valves above, jetting removes the need to bring a tip down to the part, so cycle rate is set by jet frequency rather than axis travel. [3] [1] [2]

Editorial calculation: 0.3 MPa is about 44 psi; at 1,000 dots per second the valve could place 3.6 million dots an hour if fed continuously.

Give the fluid viscosity at dispensing temperature, dot size or volume, dots per part and required rate, and ask whether a needle, diaphragm or jetting valve suits, with tested results on your fluid.

04

Consider a volumetric rotor-stator dispenser when volume must not drift

Time-pressure valves meter by open time and pressure, so the deposit moves with viscosity. preeflow, a ViscoTec brand, describes its eco-PEN dispensers instead as rotating, pressure-tight positive-displacement units with a self-sealing rotor and stator (its "endless piston" principle), conveying fluid by displacement in the stator so that dosage is independent of viscosity fluctuations, with programmable suck-back or reverse flow to cut off the thread without dripping. It lists dosing pressures of 16 to 20 bar, a smallest dispensing quantity of 0.25 µl, dosing accuracy of ±1% and repeat accuracy above 99%. [4]

Editorial calculation: on the eco-PEN300, a 1 µl (0.001 ml) shot takes about 0.5 s at the lowest listed flow of 0.12 ml/min and about 0.04 s at 1.48 ml/min, so the shot volume and the cycle time together decide which model size fits; the XS 180's 0.25 µl minimum is still 250 times the 1 nL minimum droplet Mycronic lists for its piezo jet. [4] [3] Ask for the flow at your fluid's viscosity, the stator material in contact with the fluid and its replacement interval.

05

Valve families on the listed makers' sites

Listings include needle, pneumatic jetting, piezo jet and screw valves, dispensing valves sold with adhesive pumps and two-component systems, and valves supplied as part of automatic glue dispensing machines. Ask each for the wetted materials, rated pressures, cycle rate and a dispensing test on your fluid.

06

Piston, spring, needle or diaphragm: parts of a pneumatic valve

07

Fluid and cycle data to send with the enquiry

Rows quote the EFD needle valve, the Fisnar diaphragm valve or the Mycronic jet where their documents give a figure; electrical rows depend on the controller you pair with the valve.

08

Send the fluid, deposit and line data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Fluid: [name; viscosity; filler; cure type]
Deposit: [dot, bead or fill; size; tolerance]
Speed: [dots per part; cycle time]
Feed: [syringe, tank or pump; pressure]
Tip: [gauge; length; access]
Control: [controller or robot I/O]
Test: [trial on our fluid]

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