PR combination valve

Hi looking for general info with regards to the need to fit a PR combination valve group on an indirect unvented cylinder.At the incoming main we have fitted a PRV that takes the pressure down to 3.5 bar from 8 bar
As the Indirect cylinder will receive incoming pressure at 3.5 bar and we will fit an expansion vessel and expansion pressure relief valve on the expansion vessel. The balanced cold feed is already balanced by the incoming main PRV. So do we need to fit the combination unit as well?
Many thanks

 

Thanks for your response and yes we will go with having the two PRV's it appears that just using the main will work perfectly but as you say it needs to be done to manufacturer"s instructions.Also we note that as the main is remote then there is the possibility of adjustment being made without it being locally We will set the main PRV at 4.5 bar then the localised at 3 to 3.5 Bar
regards Dollar
We are also from lead pipe to speed fit and can still wipe a lead joint and patch a copper tank with a moleskin solder wipe

Regards

 

Gif to put your mind at ease we are Sparks and the plumber is G3 registered but we are inquisitive and therefore need to know. We have installed 1500 litre steam pressure vessels and pipelines and all with coded Guys so between us are aware of pressure vessels, and regs Having said that we are always keen to know more. this is a small job that has come up probably would have been better to get the Rep in. Anyway thanks for your input. Just one point in France where they have had pressure systems for years you can fit a pressure unvented tank with imm heater and stat
with a 7 bar Prv off the DIY shelf so how does that figure ?

Thanks Dollar

 

Yes indeed Peter or even take the cart from the yard with the tools and pipe on (Galv of course) and do the
jobs around the Town
Wonder how long today the tools and materials would stay on the cart?

Reg Dollar