When considering major changes to your plumbing in your home, if your plumber simply tests the Static Pressure, you will have no idea of what pressure you will get when you actually use a shower or run a tap. You need to know the Dynamic Pressure.
What is Static Pressure?
This is the pressure with NO FLOW which is just an indication of what the pressure will be when you need water. The static pressure will reduce the higher the reading is taken so if you start with 1 bar (10 metres head), at ground level, move 3 metres higher to a second floor in a house the pressure is 3 metres less (10-3 = 7 metres)
What is Dynamic Pressure?
The more water you want the greater the speed of the water in the pipes and the greater the friction loss but only to the tap that is running. This friction loss can be very significant or minimal and you will only know when you measure it. To find the dynamic pressure entering your home measure the pressure at a tap or a shower whist taking water from other taps and showers. The tap or shower you are measuring the flow will have no flow so there will be no head loss between the on the feed pipe so you can measure the dynamic pressure when flow is taken.
Example
You invite a plumber into your home and your plumber suggests you fit a Combi Boiler. The Combi Boiler will heat a maximum of 20 litres of hot water (this will vary depending on the KW rating of the boiler). The plumber measures the static pressure to be 1.5 bars (15 metres head). The plumber fits the Combi boiler and demonstrates it works by opening a tap and charges you £2500.
Later in the day the boiler stops working because pressure drops below 1.0 bars and it is now your problem.
Question One – Did you check what the dynamic pressure was when you ran 20 litres of water from your system?
Answer No – your fault because it is never a plumbers fault.
Solution
You could try to get your old gravity system and your money back from the plumber (good luck with that), or you could boost your pressure to the combi boiler.
