Hi,
We now make our own - configured to a 400 litre capacity with flow rate of 50 litres per minute @ 5 bar. The configuration is designed to give a 40kw combi it’s maximum flow rate. The pressure also ensures that on an unvented system, that too can operate at full capacity.
Before this we used Stuart Turner systems, but they were not man enough ( in our experience) to deal with three storey properties in North London - a 200 litre tank was not replenishing fast enough. None of the proprietary systems that we have seen are effectively insulated - in our experience insulation or trace heating ( for severe frost protection) is a very important requirement.
The market we are in is for people looking for hotel quality showers in a domestic environment - that is not as easy to achieve as it sounds.
With respect to ion exchanged softened water, pumps and pump seals in the accumulator have a much shorter life with the higher salt content. However, softening the water before the accumulator gives better performance ( we loose 0.75 bar across the softener), hence the need for 5 bar at the accumulator output to soften afterwards.
By softening afterwards, it also allows the kitchen tap ( drinking water) to be unsoftened, but balanced (Pressurised) with the hot water softened supply.
With respect to pump seal life, bear in mind that with an accumulator, if the pump fails the flow rate is lower than that from directly off the mains - so reliability and availability is key. We have looked at duty and standby pump arrangements, but that is not a cheap or cost effective option.
Finally, they are not a cheap solution, but once people have them, they are sold for life. We have had a lot of repeat orders for systems when people move house!
Hope this answers your questions