Negative head is where the shower head or tap is above the water level in the cold water tank. Positive head is when the shower or tap is below the water level in the cold water tank. Zero head is when the shower head or tap is the same level as the level in the cold water tank. Should the water level fluctuate, (and it will if it is a cold water tank in a conventional home), the pump may transition from positive head to zero head, to negative head.
A double boost ShowerPowerBooster is great for negative head situations, zero head situations, and situations where there is the minimum of positive head if you adopt a simple way of turning a pump on and off. Each pump takes only 12 watts of power so the transformer will not overload a lighting circuit so wired into a lighting circuit it can operate whenever a light is switched on and off even with a twin pump set.
1.0 The simplest way is to turn the transformer on and off at the plug socket.
2.0 The pumps take 12 watts each which is far less than a 100 watt light bulb so you can wire the transformer into the light switch or fan and it comes on and off with the lights or the fan.
3.0 An elegant solution is to buy a radio remote to switch the pumps on and off.
4.0 An automatic SPB will operate automatically if the Shower is gravity hot and cold or a hot tap is not a mixer tap (* see note at the end of this blog)
Automatic operation is sometimes possible in negative head situations. A ShowerPowerBooster will raise water to the height of a tap. When the tap is closed it traps water between the SPB and the tap. When the tap or shower is opened after a period of time (in excess of 18 seconds), air enters the pipework at the tap and the water back flows through the automatic SPB. If the flow switch detects black flow of water flowing it starts the pump. For this reason we recommend you buy an automatic SP21S.
Mixer Taps and Showers
Most mixer taps and showers have non return valves on the hot and cold side of the mixer in order to stop cross flow. In order for an automatic SPB to work in a negative head situation these non return valves need to be removed.
Detailed drawings and instructions are in the booklet sent with the pumps but you can download the online version of this guide using the orange link on this page.
