Pumps are devices to move fluids around, generally a pump is a combination of a motor and a mechanical device to move the fluid, the pump. We have become used to referring to the whole device as the pump, strictly speaking this is incorrect. In brewing, pumps are used to move water and wort, without them we’d have to use gravity or our own efforts to move the fluids around. Fluid pumps need to be mounted correctly, to stop gases getting trapped and damaging the impeller, we also have to drive and maintain the pump according to the manufacturer’s guidelines. Take time to consider the size of pump you need, the information below will help you understand a little more about pumps and what you might need.
SPECIFY YOUR PUMP
To specify a pump we generally consider the following:-
The motor drive.
Rated supply voltage (Volts), this is the supply voltage needed by the motor to run (often 12Vdc, 24Vdc 120Vac or 230Vac).
Rated current (Amps), this is the maximum current taken by the motor when running.
Rated power (Watts), this is the maximum electrical power taken by the motor. (in homebrewing 20W is a small pump, 150W is a large pump).
The fluid pump.
Maximum fluid temperature, you’ll want 80C for a mashing pump and 100C+ if you want to use on the Boil Kettle.
Maximum flow, this is the maximum flow the pump can achieve, sometimes in litres per minute (LPM), or gallons per minute (GPM). Consider 5-20 LPM for mash and 20-30 LPM for cooling and pump-out. On a HERMS system you may want a high flow (20-30 LPM) through the coil to speed up heat transfer and ease control.
Head, this is the distance the pump will lift, raise a fluid, in metres or feet. Generally 2 to 3 metres is sufficient, at your chosen flow rate.
Maximum pressure, this is the maximum pressure the pump will deliver.
Simply speaking, pressure and head are related, the greater the pressure the greater the head. Pressure and head are dynamic and vary with flow rate when the pump is running, generally as the flow increases, the pressure and the head will fall, as you can see above. Pump manufacturers do publish this data as a graph. For a correctly sized pump you will want to be working near the middle portion of the graph, in terms of flow and head. Pumps can be too big for the system, so bigger is not necessarily better.
OTHER CONSIDERATIONS
For brewing you need a ‘food-safe’ pump, this generally means it has a magnetic coupling, where the motor and the pump impeller are linked by magnetism, as opposed to a through-shaft.
Pump material, this is often related to its food-safe rating and/or the maximum fluid temperature, for brewing systems you will want a maximum temperature greater than 80C for mashing and 100C+ for the boiling and cooling side.
HOW TO SIZE A PUMP
If you brew 60 litre batches, and you've decided that when you are mashing you want the 60 litres of wort to fully circulate once every 5 minutes, then you need a flow rate of 12 litres per minute, if you have a pump that can deliver a maximum 24 LPM, then all you need to do is use an inline valve to throttle the flow back to 12 litres.
Some pump-words you may want to impress your mates with, ‘priming’, ‘ventilation’, ‘surge’ and ‘cavitation’.
Priming is really the introduction of the fluid to the pump so that it can be started, without damage. Many pumps use the fluid as a lubricant the cannot be run dry, they must be primed.
Ventilation is the act of getting rid of gases I the pump, this is important, as trapped gases can reduce pumping efficiency and reduce the working life of the pump. Some pumps have a manual valve to release the gases, sometimes a series of on/off cycles are used to take the gases through.
Surge is when the pump speed fluctuates rapidly, can be caused by rapid valve closure. Not often seen in small brewing systems. The driving motor tend to speed up when the flow reduces to zero, this is because they are not doing any work, simply rotating.
Cavitation is the formation of gas bubbles in the fluid being pumped, these bubbles can damage and ultimately destroy the impeller within the pump. Cavitation will happen if you try to pump a fluid near its boiling point. It can happen within the pump to the extent that flow will virtually cease, is can also happen at a restriction as the pump tries to suck fluid through, the low pressure created can allow the bubbles to form, they can then get stuck in the pump, flow can stop, the pump run dry, causing damage to the pump. Generally, as the wort approaches about 95C, it becomes impossible to continue to pump using an impeller based pump, as the cavitation really starts to limit the flow.
SAFETY TIPS FOR PUMPS
When mounting the pump, use the manufacturer's guidelines to position correctly.
Always check a pump is permanently off and all relevant valves are in the correct position before disconnecting hoses.
Always ensure hoses are firmly fixed with clips to tails and fitting, as hoses can become soft and with increased pressure the hose can detach from the tails. Always use barbed and swaged tails, and ensure hose clips are always used.
Never leave a pump input or output port open, always have hoses attached to both terminate in a vessel.
Always ensure pumps are electrically earthed and all mains leads are kept away from fluids.
Use earth leakage trips to give added protection.
When closing valves on a pumped circuit, do it slowly and if you are diverting flow, best to open one path before closing the other.
Safe and happy pumping.