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. There are plenty of simple ways of turning a pump on and off. The pumps take 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.
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 of a ShowerPowerBooster under negative head.
Non Mixer Taps
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 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. The flow switch detects water flowing in either direction and so it starts the pump and continues to pump until the tap is closed again and the flow stops (This process traps water between the SPB and the tap so the process can continue).
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.
Double or Single Boost
A SP2S or a SP1 boosting the hot only will give a single boost to the hot. Because the existing pressure is negative it is better to double boost the hot and single boost the cold by adding a SP1U to the hot.
A SP22S (or a SP1 pus a SP1U) boosting hot and cold will give a single boost to the hot and cold. Because the existing pressure is negative it is better to double boost the hot and single boost the cold.
A SP21S costs £155 gives 1 automatic pump, 1 slave pump, and a 5 amp transformer.
Contact us if you need further guidance.