beattsmjk
Mechanical
- Apr 15, 2009
- 40
Hi,
I have searched this topic and found some useful info, but I thought I would write a post to see if anyone can offer any more specific info that might be useful.
I work in a bakery and we have two tanks of liquid yeast (consistency of single cream or slightly thinner). This yeast is stored in chilled stainless cone bottomed tanks, each holding 25,000 litres.
We have both tanks connected to a 'ring main' however we only use one tank at a time, with the other on hold. The contents are agitated at a speed of around 75rpm to prevent settling out of the product.
The yeast flows from the tank in use down to a centrifugal pump approx 8 metres away and approx 1.5m lower(NPSH) distance is ok according to Packo (pump manufacturer), it is then circulated around a 'ring main' and back into the tank through the side of the tank.
As the yeast is required it is drawn from the ring in small quantities at four points (mixers).
The problem we have is on tank changeover. At around 700 litres certain valves close on the tank in use and others open on the other tank which allow for a seamless transition.
However we find that when we reach around 600 litres remaining, the pump starts to cavitate and we lose all pressure in the ring main (normally 3 bar). We then have to manually switch to the new tank and dump the 600 Litres (which is not good obviously - approx £500 each time).
We are scratching our heads as to the cause. like I said, the pump size was calculated for the system and so the NPSH is ok. The pump people have no further ideas.
The yeast is circulating at around 4degrees.
Do you think the agitators could be creating a vortex perhaps and allowing air into the pump? The tanks are fitted with vortex breakers according to the drawings.
We have the pump running at full speed (2900rpm) it is designed for 7m3/h although we only need 4.5m3/h with pressure drops around the system of around 3m3/h this works out about right.
I really look forward to any advice you might have.
Thanks in advance
I have searched this topic and found some useful info, but I thought I would write a post to see if anyone can offer any more specific info that might be useful.
I work in a bakery and we have two tanks of liquid yeast (consistency of single cream or slightly thinner). This yeast is stored in chilled stainless cone bottomed tanks, each holding 25,000 litres.
We have both tanks connected to a 'ring main' however we only use one tank at a time, with the other on hold. The contents are agitated at a speed of around 75rpm to prevent settling out of the product.
The yeast flows from the tank in use down to a centrifugal pump approx 8 metres away and approx 1.5m lower(NPSH) distance is ok according to Packo (pump manufacturer), it is then circulated around a 'ring main' and back into the tank through the side of the tank.
As the yeast is required it is drawn from the ring in small quantities at four points (mixers).
The problem we have is on tank changeover. At around 700 litres certain valves close on the tank in use and others open on the other tank which allow for a seamless transition.
However we find that when we reach around 600 litres remaining, the pump starts to cavitate and we lose all pressure in the ring main (normally 3 bar). We then have to manually switch to the new tank and dump the 600 Litres (which is not good obviously - approx £500 each time).
We are scratching our heads as to the cause. like I said, the pump size was calculated for the system and so the NPSH is ok. The pump people have no further ideas.
The yeast is circulating at around 4degrees.
Do you think the agitators could be creating a vortex perhaps and allowing air into the pump? The tanks are fitted with vortex breakers according to the drawings.
We have the pump running at full speed (2900rpm) it is designed for 7m3/h although we only need 4.5m3/h with pressure drops around the system of around 3m3/h this works out about right.
I really look forward to any advice you might have.
Thanks in advance
