PUMPS & PUMPS

Again I have been asked what pumps I use in our system and I thought that I should put pen to paper this time and divulge the practice I have adopted over many years and how I got there. I use 2 types of pumps one type is SUBMERSIBLE (Centrifugal) which feeds my trays and boxes and the other is a DIAPHRAGM pump and so let us consider the Submersibles first.

1. I use all 240 Volt units for the simple reason that it is very easy to obtain 240V digital timers cheaply and that satisfies the control side of the pump and the other advantage is that they are readily available in all sort of configurations. The service side is also good generally lasting for years without problems. They all seem to have flow rate adjustments on the pump which provides easy trimming of the flow rate to suit your application.

There is one disadvantage using that type of pump as generally they have a very low head (Pump Pressure) and one has to do some maths to be able to obtain the correct unit.

For example I have a tray system consisting of 4 trays 3 m long and I want to use them in a NFT configuration to grow greens. The desired flow rate per tray is somewhere in the order of 1.5 L /min so I would be looking for a total flow of 6 L /min or 360 L / hr. Now there are many pumps that will deliver that volume on the market however we must consider the designed head of the pump.

These centrifugal pumps are generally rated, for example Pump 500 L/hr. at a Head of 1.5m. That means that at 0 head or in other words at the lowest solution level it will pump 500 L /hr. However at 1.5 m head the flow stops, so if your trays are set at 1m height for example you will pump only typically 200 L /hr. using this pump [example (Fig 1.)]. In that case you would have to go to a higher HEAD and control the additional flow by reducing the intake orifice on the pump to get back to the desired 360 L/ hr., in any case it is prudent to have additional flow and restrict where necessary by valves.

Submersible PumpSubmecible Pump

2. I started out using a 240V Diaphragm pump initially because I wanted access to cheap 240V digital timers for good flow control and the use of 12V units and batteries left me cold especially when it was suggested to use old car batteries (I can’t lift them these days).

I was rudely awakened when the supposed 3000 hr. pump life (in my case 5 years of intermittent running) came to an abrupt end when the brushes wore out in 18 months. The pump itself was about $300 and replacement brushes cost a further $80 and then you had to fit them (try that without the proper tools on a wintery Sunday). All of a sudden 12V pumps were interesting again and a better alternative to batteries had to be found.

About that time eBay was advertising cheap 12V pumps from China and a few years ago they were selling for about $60 (Ex China before freight US10.00 at that time) and these days they are still under $100. These pumps were basically produced for the USA & English markets and were rated typically at 10 -17L/min that is roughly 1-4.5 GPM and these days the volumes have slowly increased as they tend to satisfy the caravan industry to pump fresh water in vans and similar applications.

I have used 2 of these pumps for 3-4 years without the smallest problem. I supplied power to the units initially using a small battery charger however these days for a fraction of the cost I use 240V to 12V, 5-7 Amp DC Transformers which you can buy now starting as low as $12.00 on eBay. The pumps I use are 10L /min flow rates at 17 psi drawing a current of 2.2A and another unit 12.5L/min at 35 psi and drawing 7.0A. The low pressure unit will operate SmartValves and I use one to feed various pots / plants located around the property with runs in 13mm Poly pipe up to 20 metres.

The other unit is used to feed all the greenhouse pots (40) growing tomatoes, cucumbers and capsicum and is run open ended to obtain maximum flow at very short run time of 3-5 min on an hourly bases.

Both of the pumps are approx. 200mm in length and a smaller unit is available at 160mm and may be suitable for very small applications but I have no experience with that pump myself.

A big advantage with these pumps is the ability of quick change over if the pump has to be replaced by the use of rubber ring seals and quick lock arrangement.

A typical diaphragm pump and fittings are sho

WPFL40

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