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In The Winery Three friends and a bucket...


Pumps come in a variety of types—the choice depends on what it should do, and not do. By Gary Strachan


R


ecently, I had to consider the specifications for a pump — displacement, capacity etc. I thought about how much I must have moved from a fermenter with a bucket and how long it took.


Here are the fundamentals. The displacement for a bucket is about 20 litres, about 15 litres if you allow for not quite filling the bucket (cavitation losses). With a three-person chain between tank and press we hit a top speed of about 30 seconds per bucket, about 30 litres per minute.


If someone held up the line, the line stopped. A positive displacement pump would have just built up pressure until the electrical breaker tripped or the line blew apart. I’ve seen some spectacular blowouts when a positive displacement pump stream was blocked by a closed valve.


There are several kinds of positive displacement pumps. They’re nice to use because you don’t have to prime them. They even handle fermenting wine because a large bubble doesn’t lock them up. On the other hand, there are certain things you DON’T DO.


Don’t use a positive displacement pump for filtration unless you have a pressure bypass valve. If the pressure builds and the flow rate declines, say goodbye to your filter pads or cartridge and be prepared to filter the batch over. Don’t run a positive displacement pump dry unless you have deep pockets. Some pumps, such as a diaphragm pump, can pump air but most depend on fluid flow for lubrication and cooling. Pump friction can develop enough heat to melt seals or abrade close tolerance machined surfaces.


Examples of positive displacement pumps are lobe pumps, such as Ladish or Waukeshaw; gear pumps, such as Viking; progressive cavity pumps such as Moyno; piston pumps, such as Manzini and diaphragm pumps, such as Graco. Each has strengths and weaknesses of design. There are some confusing choices until you’ve actually operated a few of them.


20 British Columbia FRUIT GROWER • Fall 2015


A flexible vane pump, with the impeller vanes extended.


The other end of the spectrum is the centrifugal pump. It’s a great workhorse but really aggravating when it locks up with an air bubble. They are like a boat propeller inside a round chocolate box. The inlet is at the front and centre, and the outlet is tangential to the edge. Product must flow to the inlet by gravity for the pump to start and the pump must have a minimum speed to initiate flow. A bleed valve on the top of the pump can help to get it primed. There are two basic designs of centrifugal pumps: open impeller and closed impeller. The closed impeller style is more tolerant of air bubbles and can typically reach higher head pressures, but it plugs more easily if you have skins, stems or seeds in your product.


Don’t ever use an open impeller centrifugal pump for a red wine pumpover unless you want to turn your skins to pudding. Centrifugal pumps are great for CIP (cleaned in place) systems because they can recirculate great volumes of water at moderate pressure.


Somewhere in between these is the flexible vane pump, such as a Jabsco. These typically have eight rubber lobes that rotate inside a circular stainless steel housing with one flattened side. The displacement is the difference between the interlobe space when lobes are flattened and when they are fully extended. It’s a clever idea for a moderately priced and serviceable pump. A Jabsco will draw enough air to usually start without priming but sometimes a dry pump requires a shot of water to provide enough lubrication to start turning. On the other hand, if you run it dry for too long, the housing can get hot enough to melt the impeller, destroy the O rings and make a terrible smell — and you may also distribute bits of burnt rubber throughout the tank you’re pumping into. It could be an expensive coffee break.


One of the best pump accessories is the variable frequency drive (VFD). In the olden days, pump speed was varied by a monster big steel casing that had an array of belts, pulleys and gears inside with a crank handle on the back. You could only change the pump speed while the pump was operating or you ran the risk of damaging it. VFDs operate on three phase-power, but if you don’t have that, they come with a small solid state phase converter.There are all sorts of reasons why you may choose to not always operate a pump at full speed, and a VFD is the way to do it. The other great accessory is a remote control. When perched on a ladder peering into a manway, I really dislike having to drag a pump control wire up the ladder with me. Of course I could always use a bucket.


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