Single Feed (Primatic Cylinders)
Blast from the Past
These were used widely up until the 1970's, as they only neeed one tank in the loft to feed the cylinder. Inside the cylinder is a baffle, which when filled, creates a trapped bubble of air. This air bubble separates the central heating water and domestic hot water.
When they were working, they were on paper a good idea. However, the problems come when the air bubble needs recharging. How does one know when maintenance is required? You get brown water coming out of the tap. This means the two waters have mixed internally.
Primatic Cylinder |
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To reinstate the air bubble is simply a case of draining the central heating system down, and then refilling. Then it's the time to cross your fingers, and hope it's worked!
With this cylinder, you can't use any corrosion inhibitor, the risk of chemicals coming out the hot water tap is too great. Because of this, systems with primatic cylinders normally have major issues with corrosion in the radiators, system and boiler.
Combination cylinders (extra tank braized on top of cylinder) can also have a primatic arrangement in the top portion of the cylinder, these are few and far between, but work on excatly the same principle, except there is an absence of a tank in the loft. These were sometimes known as 'Fortic' tanks, the brand name manufactured by Range cylinders.
If you have one of these tanks, you should seriously consider upgrading to an indirect system. Would you like to risk washing up in dirty radiator water? If your primatic tank leaks, you can no longer fit these. You have to fit an indirect replacement, which means an additional tank in the loft.