When the plunger of your syringe strikes the syringe holder block – or ‘bottoms’ out, a large mechanical load is placed on the drive motor, the drive belt, the drive pulley, the drive screw, and the pusher block, The mechanical drive train ‘stalls’. This doesn’t happen with peristaltic pumps.
Pumps come with and without stall detection.
Pumps without stall detection will continue to push against the load until either some one stops them or something breaks.
Pumps with stall detection will stall and then stop pumping shortly after. Thus preventing damage to the pump and especially to expensive glass syringes.
Bad Operator Behaviour
It is generally considered bad operator behaviour to allow a pump to stall, and worse yet is to rely on the stall detection to stop your pump. For example putting a 60ml syringe on your pump and saying go ahead, pump 100ml – relying on the stall mechanism to stop the pump when the syringe is empty.
You should be programming your pump carefully to avoid stalls and keep the syringe from extracting the plunger or striking the bottom. Some calculation is required here.
It’s Hard on Your Nut Block
Pump warranty is voided by high stalling levels. Each time the pumps stalls, the nut block is damaged, and will eventually ‘loose it’s teeth’ causing a loss of pressure. However, these nuts are a sacrificial replacement part designed to protect the other drive components. It is not acceptable to run the pump till it ‘bottoms’ out. Stall detection will ‘see’ the pump stall and stop the pump drive. The drive nuts are not user replaceable.
Without the stall detection feature, how does the pump respond to stalls?
Would the pump continue to run even though no fluid is being dispensed?
Yes the pump will continue to run and the toothed belt will slip over the gears on the motor and screw drive. This damages the gears (slowly) the belt, and the drive nut – which will loose it’s teeth and fail first by design.
Tip: Buy the stall detecting pumps.
Despite all your best attempts – there will be times when your pump stalls. If this is on Friday night after you have left a pump running for the weekend, and something unexpected happens (and it does!) a stall detecting pump will stop pumping in a moment or two and save it’s self. What ever was expecting fluid will be starved of it – but the pump will be saved. Without stall detection, Monday morning you will be sending a pump away for repair.