That depends on the system design. If it's an S-plan where all the zone valves will be closed, then yes you need a by-pass. If it's a Y-plan with a mid-position valve, there is always a path open somewhere - unless *all* the radiators have TRVs (at least one of which shouldn't have!) and they are all closed.
Wouldn't a slow release relay/contactor be suitable?
You can buy variable delay relays from RS etc, but they're far more expensive than making your own.
I used a multifunction electronic staircase timer (RS 277-3520) - £18; for a similar application.
It seemed to me that by the time I had bought the bits, put them together, got a small power supply, put the whole lot in a box, it would approach this on parts before considering the time taken.
.andy
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I was basing my view on the fact that anyone capable of making such a thing would very probably have many of the parts needed simply lying around waiting to be used. Or perhaps that's only me. ;-)
Fair point. Yes I know what you mean. I have boxes of components where I have to look up the part number to remember what they are.
.andy
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In message , Andy Hall writes
I do hope you've kept some old RS catalogues from the days when they used to print their part number on ICs etc, I have.
Aah - so it's not just to give a 2 min delay then, I'll let you off
I was surprised that they are still printing the paper catalogue, but they do. I had a package with half a tree in it from them the other day.
Regarding legends on ICs, this reminds me of my early career, designing control systems for mobile radio applications using some of the early microprocessors. The only suitable options for program storage were bipolar proms, which at the time cost £35 each for a
1kbyte one. Since these weren't eraseable, it did mean that you checked your code. Even so, we got through hundreds of them...For the interface logic, it was necessary to vendor select because some vendors components, although meant to be identical, were made by a different prduction process slightly and the radiated RF from them could vary considerably.
There were interesting tales here, because as design engineers for the product, we held the authority on which vendors were approved and which were not.
One vendor, who shall remain nameless, but whose logo is a bat wing symbol, had one of the cleanest ranges, RF-wise. Unfortunately, in the countries of the middle east where a lot of the products went, that particular vendor at the time, was very definitely persona non grata. To get around this, we sourced the self same components from RS which had had the logo removed and the RS one on there instead.
Another vendor shot himself thoroughly in the foot by the way that he operated. The smarter reps would come in and visit the engineers and discuss their projects as well as introducing new products. They brought data books, of course, and the really smart ones would ask about the "homers" that engineers might be doing. Samples of suitable components would then appear in the post or on the following visit. Occasionally, they would invite a group out for a pub lunch which was always appreciated.
One particular rep really hadn't checked into how the game was played. He had made numerous visits and a few of his products had been designed in. However on one particular occasion he showed up just before lunch with none of the items promised previously and then made a thing about having to rush off to take the buyer for lunch. By the time they returned, the few qualified items had been deleted from the approved list. Despite the later protestations of the buyer, the vendor never did sell anything into this product range.....
.andy
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I *think* the website will give details of any obsolete part number - or it has for those I've tried. And the fast find part of the cat does as well - although of course I've not done an exhaustive test.
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