Rotthenbugger crapoflush

[Paul Barker]

Have always been a little dishartened by the abilities of my Rottenbugger, but yesterday took the biscuit. It's another one of my long stories I'm afraid.

I had to change a pump on an alpha boiler because flow lockout occured. This seemed to fix it. Then yesterday I got a call back, it's doing it again, now I have to go back and find out what the real problem is. That's another story, but trust me it isn't sludge, the system is brand new, underfloor heating all in plastic with brand new boiler and there is an auto bypass.

But anyway, I thought I'd check out the 15/60 which came off it last visit, rigged up a plasterers bucket full of watter and pumped it using the 15/60 into a bucket. It filled a bnq bucket in about 10 seconds through 22mm pipe.

Well impressed I thought, noubt wrong with that, there is definately something else going on.

Out of idle curiosity I got out my powerflush, and saw quite clearly that it doesn't have as good a force as the Grundfos 15/60, not far behind, but if it is to do it's job it wants to be a jolly site better.

In short if you just fill the system again with fx2 in it, and turn off all rads but one and shut bypass your CH system pump will more than likely do the job. Changing rads etc etc.

So then I took this weak specimen of a uselessflush apart only to find there isn't much in there worth more than tuppence halfpenny powered up by a £25 motor.

So I had a look for more powerful machines, these cost geting on for a grand and are no more expensive to make barr the additional motor size which probably costs them £75.

I know what lets all rip off plumbers they are rolling in it.
The fols selling us budget (£<500) powerflushes are conning us because they can't even make something as effective as a CH pump, and the ones making the good ones want about 500% profit.

 

[HarrogateGas]

I use the Sentinal Jetflush 4 machine which is power by quite a collosal Grundfos pump.

ve had a play with it in the past and it can generate about 2.5 bar pressure on a average system. There isnt much that it cant shift and i though £800 for it was a pretty good deal.

 

[Balenza]

You should try fitting about 20m of 15mm pipe to the outlet of each pump and see which one delivers the most flow.
Are powerflushers not designed to maintain pressure. ?
Large motors etc and different design of the vanes on the impellar.

I have a submersible pump and it will deliver about 200L/min with 2m of 50mm pipe on the outlet.
Using 15m of 15 mm it drops to no more than 15/L min

 

[Paul Barker]

Looking at the way it's made there is no way it can maintain pressure, the humble CH pump is better equiped for the task.

The powerflush has two circular disks that clamp onto a starfish arrangement bye directional obviously. The pipes from the outside join on to a collector each, but there is a small hole where the interface is such that any excessive resistance results in the machine bypassing the oulet and just pumping the water around inside itself, therefore it is a pretty ineffective design if delivering water at pressure is your objective.

A powerful lift pump which is incorporated into the sealed system using a matrix to change direction would be far more effective for the task.

Incorporate a bleed point to purge the system and a fill point. The inlet of the pump could actually be fed from a break tank, the return could either drop into this tank or be diverted to a drain. The break tank to be refilled from the mains.

I'll probably build one instead of spending £800 on a manufacturers part.

 

[Balenza]

Connect three circulators in series and triple the head delivered.

 

[Paul Barker]

Yes I thought so.

 

[gas4you]

I was taught that powerflush machine is high flow low pressure an the Sentinel course, which is why it is not very good for microbore

Now I'm confused

 

[Paul Barker]

Certainly a 15/60 is superior to my piece of con artistry. Not only has it more flow volume but the so called powerflush bypasses excess pressure internally, an in line pump can't do that.

I am quite clear in my mind that to follow the same principles using the system pump is superior to this machine. Then flush out the chemical with a mains flush. You have the added bebefit that boiler heats chemical Fx2 works best at >40°C.

 

[ChrisR]

The sentinel, and maybe others, is designed for the pressure not to get too high, for fear of bursting things. Hence things like holes.
To get lots of flow you need a whopping pump, but that would be capable of a lot of pressure when flow zero.
So it needs a thing a bit like an auto bypass valve. Or, so they can flog it for £800 and make a profit, a hole.

The Fernox people used to say their machine would give 3 bar, but now they're saying 1.5 or so, so maybe they had to nobble that, too.

I bought a pump for £25 which is capable of 80l/min at 3 bar - one day I'll try it!

 

[Paul Barker]

Yes I was gutted when I saw that there is effectively an internal pressure limiting bypass (a hole in the fickin thing).

You give me an idea though, in our better design we can simply put an autobypass into the system.

But we are now back to the realms of simply leting the system pump do the work as we go round the house turning off all rads but one. Exactly the same as we do with a machine. We dio this in the first instance anyway don't we all? when we get called to a "some of my radiators don't get warm." Or when we have filled up and one leg doesn't get warm.

So we are now left with the only remaining advantage of a powerflush that it is bydirectional. Well this is actually one of it's design flaws. Because it changes flow direction by reversing the motor the impellor chamber design is suboptimal. The two exit pipes are close to each other, if the return is not connected into a closed loop with the flow water is actually pushed out of it, so it adds no effort to the flow. Whereas your CH pump pushes and pulls by nature. Therefore you would get far greater effect from a given motor using either a pump for each direction or the matrix of valves you have drawn for us before Chris. I think I'll just mount two pumps. I have two like yours Chris.

So that's two pumps, two autobypasses a break tank with a pair of float valves and AA gap, and a pair of draw off points for dump valves.

Probably a pair of 15/60 pumps instead of the lift pumps would be superior as no worry about overdoing it. The pumps thee and me have might be too powerful.

 

[DP]

Paul the pump on a Fernox machine is quite large. While have not measured flowrate, large (long) pipes seem to effectively deliver power

 

[Agile]

Chris's pump can give 3 Bar and it can also give 80 li/min.

But it cannot do both together.

The best test of any pump is to measure the flow rate it will give whilst maintaining a pressure of say 0.5 Bar.

talking of pumps it was interesting to hear this morning about the one which failed in Scotland with an Archimedes screw. A big one I expect!

They had a repair kit with bearings and seals etc. but other parts of it had failed. The kind of problems we sometimes go to!

Tony