Modules Behaving Badly

Written by Peter Ridgers (Crafers CEO)

The hot adhesive module is a precision built  mechanical device that accurately delivers  Hot Adhesive via a nozzle. The module often gets the blame for misbehaving when in fact a poorly operating module is in fact trying to tell you something. It is all to easy to blame the module. 

Does this sound familiar. ” Mr Fitter the box is not gluing ? No glue coming from the module better change it out . A new module and nozzle are fitted and the problem goes away for a while.

We did a study on misbehaving modules and found the following faults to be the most common complaint:

  • Module not operating.
  • No or little adhesives coming from module nozzle.
  • Module slow to open.
  • Module slow to close.
  • Adhesive weeping through the center weep hole.

In most cases the module had misbehaved after 4 to 6 weeks of operation. Why the failure? 

  • The first thing to establish is, has the misbehaving module been fitted to a new or old / existing hot adhesive heater block? 
  • What adhesive is being used?
  • What are the operation specifications of the adhesive?

Adhesive s play a major roll in the performance and life span of a module. The better the adhesive the less the gel / char, the greater the module life.

The greatest enemy to a module is Char or Gel.

Please read the comments carefully as each statements could cause a module to fail and what can go wrong when fitting a new module to an old heater block.

Causes of Module Failure:

1. Heater Block

The heater block is 2 , 3 ,4 or more years old and was last serviced ? Module Heilcoils could be stretched or damaged causing a module to leak between the manifold and heater block.

The heater block has heated and cooled many many times making the inside of the heater block a perfect environment for the growth of gel and char.

The heater block has machining dead spots, these are places that trap hot adhesive and act like a back water. Adhesive will burn, degrade, and gel in these dead spots.

2. RTD Sensor

The RTD ( resistance thermal device ) sensor has a life span, we suggest 2 years. When the  RTD sensor has failed and needs to be changed . The fitter will more than likely use ceramic nuts to join the RTD electric cables . 

A good cable join should have little to no resistance BUT over a period of time with the heating and cooling of the heater block the cable joint deteriorates and  a resistance forms within the joint. This resistance will cause false temperature readings at the gun.

3. Air Valve

The air valve needed to operate the module has become lazy over many operations. This may result with a restricted air flow into the module. The result  a slow module opening.The same can be said for the module air exhaust.

  • A restricted air flow will result in a slow module shut off.
  • The air valve needs to give a clean burst of air at 5.5 to 6.5 bar.
  • The air valve needs to be capable of excepting exhausting air at 180 c .


Many a problem can arise from the incorrect air valve being fitted to a hot adhesive gun. Modules has been changed, when in fact the air valve has been at fault.

4. Piston Pump Air

Remember that  1 PSI of air pressure gives you 14 PSI of adhesive pressure on a 14 to 1 pump and 1 PSI of air pressure gives you 20 PSI of adhesive pressure on a 20 to 1 pump.

  • Acceptable pump air pressure will range from 15 PSI to 50 PSI . This equates to the fluid pressure of a dual action piston pump to be between 210 PSI and 700 PSI
  • A correctly operating hot adhesive system will have a fluid pressure ranging from 200 PSI to 600 PSI . 
  • A pump pressure over 600 PSI could indicate a fault in the melter ,hose ,filter ,gun heater block and module or nozzle.


I have established that un-serviced melters,pumps, hoses and gun bodies will more than likely have one or more faults. 

So why does an unserviced Hot Adhesive System cause a module to malfunction?

  • Contaminated adhesive may enter the module glue chamber. This may result in char being lodged between the needle and seat .This will  result in a needle and seat leak or a blocked nozzle


  • RTD giving false readings to melter. The heater block and module temperature could be plus or minus 20 deg from the melters set point display. In the case of the temperature being greater than the set point , the adhesive will start to burn, gel or gum this may result in a poor adhesive flow from the nozzle. 


  • More adhesive is required so the fitter turns up the pump air pressure. 60 PSI at the pump means 840 PSI at the module.


  • Higher temperature inside the module has changed the adhesive viscosity. The adhesive now thinner puts extra strain on the module seals.


  • Still not enough adhesive so the fitter ups the pump pressure to 65 PSI  module pressure now 910 PSI.


  • The boxes are now sticking. How long can the module seals that are designed to operate up to 700 PSI last ?Five weeks later and the new Module fails . Is replacing the module going to fix the problem?


I can write this story on the miss behaving module 3,4 or 5 ways and the conclusion is always the same. The solution is yearly servicing combined with using a good adhesive.

Modules Misbehaving In A New Gun

Now let’s talk about why a new module will misbehave in a new gun. Not common but we have had reports were a module has failed on a new gun after 2 or 3 months of operation.


The New gun is fitted it an old hose. Adhesive flow through the hose is poor . As the module is the exit point of the adhesive the module shows a poor flow of adhesive. Fitter says change the module.

A new gun is fitted to an old air valve. The Air valve has restrictions and can not supply sufficient air flow to allow the module to snap open.As the module is the exit point of the adhesive the fitter says change the module.

A new module fitted to a new multi module gun has been connected to a hose and heated . The current operation does not call for all modules to be used.The air valve to the module is switched off. Over time the module heats and cools. Non flowing adhesive inside the module starts to gel.

The module is now called upon for use as the new operation requires this module to be used.The module operates but is lazy. Fitter says change out the module. All is now good. Has the fitter fixed the problem?

In this case the fitting of an extra hose and gun that can be switched off when not in use would have been a solution.

The next time your module starts misbehaving badly ask the question ? Why? In most cases the failed module is trying to tell you Hay somethings up here.It is very rare for an Industry Standard module just to fail for no apparent reason.



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