Microbreweries

Pumps For Microbreweries One of the biggest problems small brewers have is pumping hot wort from the Kettle. The problem manifests itself in continuing seal failure on centrifugal pumps used for the transfer of wort.

Why do we get this problem? To explain this, we first need to understand in simple terms, some of the basic principles behind the operation of a centrifugal pump. All centrifugal pumps need a certain amount of positive pressure at the impeller as the action of the liquid being ‘spun’ out from the centre to the outside will always cause a drop in pressure. Pump manufacturers are aware of this and publish figures for each model of pump that show the minimum amount of pressure each pump requires at different flow rates, known as Net Positive Suction Head or NPSH for short. If a pump is used below this minimum pressure, then an effect called ‘cavitation’ occurs. Cavitation is where millions of small bubbles collapse on themselves or ‘implode’ causing severe damage and vibration. Many boat propellers suffer from the same problem and are eventually worn away and need to be replaced.

How does this affect me? Unfortunately your application has all the criteria needed to cause cavitation in your pump, usually resulting in the failure of the seal causing the pump to completely fail.

1) Temperature.

                         

The liquid you are pumping is at or near boiling point. This means that there isn’t any pressure available in the liquid to help the pump and when the pump tries to take that pressure it in facts lowers the boiling point of the liquid and creates steam in the pump and cavitation.

 

2) Little height above the pump

                                                 

Many microbreweries have their kettle mounted in such a way as to give less than 1 metre height above the pump. Any height above the pump gives positive pressure and will help prevent cavitation in the pump. To make matters worse, as the kettle is emptied the height above the pump decreases making the positive pressure even less.

 

3) Pipework and filters

 

Any flow through pipework causes a loss of pressure (friction loss) and once again this reduces the pressure available to the pump. If any filters are used before the pump, they cause a loss as stated above, when they start to block they can produce large pressure losses that will cause major pressure problems for the pump.

 

What can I do to make the pump last longer?

 

Improve all of the above in an ideal world. Most pumps require around 5 Metres head (1/2 bar or 7.5 psi) on this application. Based on the fact that you will need a minimum of 5 Metres pressure head, the only options are as listed below (1) Raise the kettle at least 5 Metres above the pump. (2) Pump at a temperature below 98 deg Celsius (3) A combination of the above. In many situations it is not possible to change any of the above as the installation is already there. In this case it’s just a case of making the best of a bad situation and accepting that seals may need replacing on a regular basis. By monitoring the pumps and not letting a leaking seal go on for too long, any expensive damage to the motor is avoided.