When it comes to shower pumps, the most common question we get asked is 'What Is A Negative Head or Positive Head Pump?'. There can be many complicated terms when installing a shower pump. Getting your head right is key one. Pun intended.
What is Head Pressure?
- Zero Head is generally considered to be 600mm below the water level, as there will still be very poor flow above this level.
- Negative head, also known as negative pressure, is where the outlet is above the zero head level and there is poor natural flow of water.
- Positive head on the other hand is when the pump outlet is below the zero head level.
Overall, where an outlet is above the zero head level, or natural water flow is less than 2 litres per minute, it should be considered to be in negative head.
How does this work inside my home?
In a traditional home with a water tank, the water level in that tank is your start point. Your outlets will be your showers, taps or toilets. If any of those are above the water level, they are in negative head. If the outlets are below that water level, they are in positive head.
Of course, this head designation isn't always permanent. The water level in the tank will fluctuate when you use water in your house, which means your outlet could easily and quickly transition between negative head and positive head.
So, what's the difference between a Positive and Negative Head Pumps?
First off, simply, a positive head pump is designed to be used in positive head only, and a negative head pump in negative head. From a technical standpoint, a positive head pump needs the aid of gravity to kick-start it into action. Negative head pumps do not need a trigger.
In this way, Negative Head Pumps are also described as Universal Pumps because they can work in all situations.
Flowflex In Line Micro Pump
The Flowflex In Line Micro Pump is a unique, compact micro-pump that can be fitted by any DIY enthusiast or professional installer. It plugs into any household socket, uses a fraction of the energy of other pumps and can be used in positive head and negative head.
In negative head situations, the Flowflex In Line Micro Pump is great because in automatic mode, it will still be triggered by a very low flow rate (1.5 litres per minute). If you have a flow rate lower than this, there is an option to bypass the automatic setting and have both pumps running on manual which will handle any flow rate.
There are a few variations of this product, but in most negative head situations you will be looking to boost a very low pressure hot feed only. In this case, a double boost is your best bet, so check out the In Line Micro Pump - Automatic and Manual Pack. If you don't need that much of a boost, you can explore putting a single boost on that feed using just one In Line Micro Pump. If your cold feed is also in negative head, in most cases this will just need a single In Line Micro Pump to complete the fix.