"Pete C" wrote in message
...
On Fri, 24 Sep 2004 11:45:05 +0100, "IMM" wrote:

A cheap plain direct cylinder can be used. One with a shower tapping on
the
side for the flow from the boiler, and have two tapping at the bottom
(Range
have these mostly as standard) One bottom tapping for the return to the
boiler and one for the return from the plate. the draw-off at the top is
the
flow to the plate. Have two strap on cylinder stats to prevent boiler
cycling. The top stat set to approx 65C and the bottom to approx 70-75C.
A
relay is required using these and latching is required. When starting
from
cold the store heats up and the boiler is cut out when the bottom stat is
75C. The store cools as water is being drawn-off. Only when the water
at
the top is below approx 65C does the boiler cut in. Then it heats the
whole
store all in one long efficient burn. No boiler cycling on a few degrees
as
with one stat.

Hi,

Would that only be OK for a vented system?

Yes. Just have a stadard CH F&E tank top the heat bank up.

What pressures can sealed
systems

Sealed systems operate at approx 1.5 to 2 bar and a max of 3.5 bar, the
blow-off setting.

and direct cylinders operate at?

There is grade 1, 2 and 3, with grade 1 being the highest.

Grade 1 cylinders, the highest pressure are rated at 2.5 bar working
pressure and a test pressure 1 bar above that.

Also I wonder if it's possible to put a blending valve in so that
primary water from the boiler is used by preference, with water from
the heat bank used when necessary.

I don't quite get you. Best let the boiler heat the cylinder using a
blending valve on the flow/return, that only alows 75-80C water enter the
top of then cylinder. Heats up top down.