What's the difference between a Standard (Positive) and Universal (Negative) pump?
Knowing whether to buy a Standard or Universal shower pump is really important - the wrong choice could mean that your shower pump simply wont work.
To understand which type of shower pump you need, it helps to understand a little about how these pumps work.
Standard (Positive) Shower Pumps
'Standard' pumps use a simple flow sensor to detect the flow of water through the pump head and shower outlet due to gravity alone, that is, without the pump running.
It is the sensing of this gravity flow that is used to automatically switch on the shower pump.
The actual gravity flow required to operate a given 'Standard' pump varies across our ranges as follows:
- Monsoon - 0.6 litres per minute (approx)
- Showermate - 0.8 litres per minute (approx)
These figure are typical, but to provide an adequate margin for reliable operation, we would suggest that a gravity flow of at least 1 litre/min is required to ensure that a 'Standard' pump will switch on and off reliably.
For example, it isn't unusual for a small build up of limescale in the shower head, or a small 'kink' in the shower hose to reduce the gravity flow enough to stop a 'Standard' pump from switching on.
Some manufacturers refer to pumps which simply sense a certain flow due to gravity as 'Positive head' pumps. Stuart Turner uses the alternative description of 'Standard' because even if there is a clear 'positive head' ie the water storage tank is located higher than the shower head, many modern thermostatic shower valves restrict gravity flow to such an extent, that a 'Positive' head or 'Standard' shower pump will not operate.
Universal (Negative) Shower Pumps
Stuart Turner 'Universal' pumps are designed to function under both Positive and Negative head conditions. That is, they will function even if there is no flow through the pump or shower head due to gravity alone.
This is because they rely on a pressure sensor that detects the drop in pressure between the pump and the shower head when the shower is switched on.
New and replacement shower installations
If you are planning a new or replacement shower installation and are unsure if there will be a gravity flow from the shower head of at least 1 litre/minute, always opt for a 'Universal' shower pump!
How to measure the gravity flow
Measuring the gravity flow from a shower head in an open vented/gravity plumbing system is easy - simply place a bucket under the shower head and using a kitchen measuring jug, measure the amount of water collected in 1 minute!