Tank Vac logo
 

 

THE TANK VAC AND RAINWATER COLLECTION

RAINWATER COLLECTION; RAINWATER HARVSTING; RAIN HARVESTING; COLLECTING RAIN;

WATER COLLECTION

 

These are all terms used to describe the collection of rain and to store the collected water for later use.There are a number of types of storage tanks; concrete block, poured concrete, polyethylene, fibreglass, plastic lined wooden tanks, flexible bladder and earthenware pots to name a few.

Rainwater is free, usually of very high quality and is delivered directly to your roof. All you have to do is collect it.

Rainwater is richly oxygenated, will sparkle and bubble, is easy to lather, and will store for extended periods.In the area of New Zealand where I live we have around one and a half metres of rain each year. That is 1500mm. This rain falls fairly evenly right throughout the year apart from February and March which can be quite dry. I have a 200 sq metre roof area so the volume of rain that I receive is calculated by multiplying the rainfall in mm by the roof area in sq.m. That is 1500 X 200  = 300,000 litres.

Yes 300,000 litres of high quality water delivered free of charge directly to my roof, available for collection and use!!

To collect this water I run pipes down from the spouting along under the house where they empty into a 4000 litre concrete tank which is placed in the coolest position which in our case is the south side of the house. We have encouraged growth of ferns and native trees around the base of the tank so as to cut off any direct light. The tank is sealed to prevent entry of mosquitoes. I draw water from near the base of the tank, about 200 mm up, using a pump which pumps water to a smaller 1000 litre tank which about 6 metres higher than the house on a small rise. From this tank I run water back into the house, using gravity through a 20mm pipe, and this pressurises our water system. In the time of power cuts we always have water. There is no pump activating in the middle of the night as the pump from our main tank is manually controlled. This is a foolproof system which I fully recommend where there is a slight rise on a section.

DEVELOPMENT OF THE TANK VAC UNIT

One morning my wife Lois asked why our water tank did not overflow from off the base. As she pointed out, a base overflow system should keep the base of the tank clean and when the tank was filling the new freshwater would be retained while the older water was flushed out from the base.

Could it be done? A quick trial using a plastic drum with some 20mm pipe proved that an overflow could draw water from the tank base.

We needed to have a system engineered so that the Tank Vac could be installed into a full tank all from outside of the tank.

At Waikato University Engineering staff under the direction of Dr Michael Walmsley carried out the necessary research require to establish the best design for the system. At Waikato University there is a very modern large scale laboratory in which the development and testing was carried out. What size should the pipes be: what direction should the vacuum holes point; what size should the holes be; how many holes; how to control the overflow so that the tank level did not fall below a particular level; how to package the unit for delivery by NZ Post whose maximum box length for Rural Delivery is 1.4 metres.

These were the initial questions we needed to answer.

In conjunction with Dr Walmsley’s team, Dr David Bryant of the Auckland University of Technology, Microbiology Department, became involved with a view to discovering what the effects of Base Overflow would be on the water quality within a tank. Six test tanks were chosen and these were concrete and polyethylene tanks in the Warkworth area, the Waitakere area and south of the city. Dr Bryant took 2 water samples from each of the 6 tanks. One sample was collected from the sediment/water at the tank floor. The other sample was taken from the water just under the surface at the top of the tank. Dr Bryant was particularly interested in the levels of E.coli within the tank water. E. Coli is the indicator organism of faecal contamination.

The average level of E.coli in the water samples taken from the base of the tanks was 450 E.coli  per 100ml of water.

The average level of E.coli taken from the water near the surface of the tanks was 130 E.coli per 100ml of water.

By this time Dr Walmsley’s team had the first Tank Vac units ready for trial and a unit was placed in each of the 6 tanks being used in the trial.The researchers waited until there had been a very heavy weekend of rain and then revisited the test sites and collected water samples, again from water at both the base and from near the surface.

When the samples were analysed again in the Laboratory at the AUT the results were for Lois and I and the Engineers very surprising. Not so for Dr Bryant, who had expected the results he obtained.The level of E.coli at the base of all the tanks was zero.The level of E.coli in the water from near the surface of the tanks was also zero.

So why had this happened? It was for us an amazing result.

The answer was from Dr Bryant that the E.coli had simply died off. The E.coli in a water tank is dependent on a constant nutrient source. In a water tank the nutrients are released by bacterial colonies which form on the sediment that settles on the tank floor. Remove the bacterial colonies through the action of the Tank Vac unit and out go the providers of the nutrient stream so needed by E.coli. Without the nutrient source the E.coli die off overnight.

The Tank Vac system would also remove Giardia, Cryptosporidium and Salmonella. The tank water would be much safer for human consumption. I had noticed that when pouring a bath there were large numbers of bubbles that rose to the water surface directly under the taps but with some forming a third of the way down the tank.

At Waikato Uni some oxygen level monitoring was taken and this showed that where there was a Tank Vac unit the tank water could contain up to 200% more dissolved oxygen.

Dr Bryant who uses tank water in his Karekare home had an arrangement with a contractor where his water filter was replaced every 2 months. Dr Bryant was phoned by the contractor who asked if Dr Bryant had changed the filter himself as it appeared brand new but was theoretically ready to be changed.  

Dr Bryant realised that the Tank Vac was having a significant impact on filter life. Under normal circumstances a pump will draw into the water stream particles of plant material which are ground up by the pump mechanism and then pushed directly into the filter. It became apparent that with a Tank Vac installed the life of the filter was significantly increased. So it is quite clear that base overflow has a direct impact on the quality of tank stored water.

For those people who have batches with water tanks it is nonsense to go away on holiday only to drink water that may well be a few years old, devoid of most dissolved oxygen and with odours and tinting. This tinting and tainting of water is caused when the bacteria break down plant material releasing lignins and tannins directly into the tank stored water. Pohutukawa stamens will cause a sweet odour and a reddish colour both of which will not occur with a Tank Vac unit periodically clearing the tank base.

So for anyone using rainwater, the use of a Tank vac unit which is easy to fit by most home owners, is quite obviously the way to significantly improve water quality.

Why allow microbes to live and develop in your tank water only to try to filter them out.

Remember the outer membranes of these minute organisms may be collected by a filter but the body fluids can often continue flowing through the tap.

Warren Agnew

Tankvac Ltd

 
                                                             

http://www.youtube.com/watch?v=e1_B9WITe94&feature=related

Tank Vac Demo

  

 

RAINWATER COLLECTION SYSTEMS

I have shown the significant benefits that can be obtained when a rainwater storage tank has the Tankvac Base overflow system installed. Further to the development of the Tankvac unit we have investigated the spouting and down-piping systems commonly used to carry water collected on a roof.

We are convinced that with the changing weather patterns rainfall can occur in comparatively heavy yet short downpours. This is certainly the case in some areas of new Zealand. Thus it is necessary to ensure that where roof-water is being collected for home use most if not all of the available water is collected. For this to happen the spouting needs to be able to carry the water that falls on the roof.

Water from the spouting must be able to discharge into downpipes before the spouting overflows. The downpipes must be of a size that allows water to be carried to and discharged into the holding tank.

Our observations, calculations and research have demonstrated the following.

Regardless of the slope or fall on the spouting the maximum water flow in commercial spouting that we have observed under laboratory conditions is 0.5 metres per second. The water from within a spouting falls downward through a unit known as a Rainhead. The rainhead is joined to a pipe which carries the water to the tank. Sometimes under the house two downpipes are combined and discharge into a larger capacity pipe. Always ensure that the total of the cross sectional area of the individual downpipes does not exceed that of the pipe into which they are discharging. Otherwise water will not flow freely, the water will back –up and the spouting will overflow causing water to be lost.  In our estimates there needs to be a rainhead for each 75 sq m. section of roof area and from that rainhead there needs to be a pipe of 80mm diameter.

In laboratory trials we discovered that our downpipe system did not carry anything like the theoretical volume of water that we had assumed it would. A significant percentage of the pipe volume was taken by air. What we wanted to achieve was nearer to 100% of the pipe volume carrying water. This is known as a full bore or siphonic flow.

So where does the air enter the downpipe system?

As water flows down from the spouting at the rainhead and into the downpipe a vortex is created, and at this point air can be drawn down into the downpipe.

Air can also be drawn into the downpipe at the point where the pipe fits over the attachment fitting on the rainhead.

So it is necessary to seal the pipe to the rainhead at this point if a higher flow rate down the downpipe is to be achieved.

The issue with the vortex formed as the water drops into the downpipe at the rainhead can be overcome.

You will have noticed the vortex that forms and drags air into the plug hole when a bath discharges. At the point where the vortex opens to the air there is a ratio between the pipe diameter and the depth of water just before the vortex draws from clear air. In a standard bathroom this depth will remain constant. At my home the discharge pipe is a 40mm and we discovered that at a depth 3 times the diameter [3 X 40] ie 120mm, the waste drew air.

In the hand-basin unit which has a 32mm diameter pipe the same ratio applied ie 3 X 32 = 96

So at 96 mm the waste pipe will draw in air.

So that if a chamber is added to the pipe system just below the spouting; and if this chamber has a depth that is greater than 3 X downpipe diameter;[ie. 3 X 80 =240] then air will be prevented from being drawn into the pipe system and the full volume of the pipe is available to carry water.   This is a siphonic or full-bore flow. The chamber requires a diameter greater than that of the downpipe.

A further point to be considered is the use of bends in the spouting system. Where a 90 degree bend is used to change the direction of the water flow it is worth considering a more gentle 120 degree system. Direct changes in water flow direction cause turbulence that in turn has an effect on the flow rate and the subsequent pipe capacity.   

 

 RAINWATER FACTS

  • Earth has all of the water it will ever have;
  • New Zealand has on average 1.5 metres of annual rainwater;
  • Tank Vac provides a safe, simple, effective, economical, environmentally friendly solution to future water requirements.

   BACKGROUND

  • Of all the water in the world only 3% is fresh and of this less than a third of 1% is available to humans. The remaining water is either frozen within glaciers, polar ice caps or deep within the earth.
  • Water does not travel to earth from outer space. As water catchments become increasingly polluted by the demands of mankind, populations face many problems caused by both water shortages and poor water quality.
  • Rain harvesting systems offer a source of pure, soft water which otherwise is often going to waste.
  • Much of the municipal water has had to be passed through a series of expensive water treatment systems leaving costly, chemically “enhanced” water for consumption.

   TANK VAC

  • The Tank Vac has been developed by Warren Agnew
  • In many storage systems, whether it be a household tank or a major storage area such as a reservoir,  a build up of sediment, plant material and microscopic life forms occurs, particularly within the lower level of the water within the holding system.
  • Through the process of decay, there is an oxygen demand which is met from the oxygen in the surrounding water.
  • This can leave the affected water turbid and lifeless. The sparkle simply goes from the water.
  • When passed through a pump plant material in the water is ground into fine particles which if not removed within a filter system show in a glass of water as microscopic specks.
  • Filters are expensive to install, require maintenance and replacement and can cause a significant fall off in water pressure within the home.

   At Tank Vac we have developed a unique system that greatly enhances the quality of the stored water.

  •  Our system can be installed into any household tank regardless of size or the water level within the tank. This patented  system uses a  pipe on the base of the tank. There are holes within this pipe. This base pipe is linked directly to a surge chamber and from this chamber water rises up the inside of the tank in a pipe that exits the tank at the standard overflowl evel.
  •  When the water within the tank reaches the overflow level the tank overflows with the water being drawn from the base of the tank.
  •  Thus the contaminated water is removed.
  •  Equally importantly, when a tank is full, the fresh richly oxygenated water that flows in to the tank, is not lost to waste  but   moves down into the tank to replace the water that will be being discharged through the overflow pipe.    
  •  During an extended dry period there is little deterioration in the water quality as the
  •  water is carrying no impurities.

 
 
[Home] [About] [Contact Us] [FAQ] [Working Movie]