# I thought 9 BAR was 9 BAR regardless what was creating it?



## garydyke1 (Mar 9, 2011)




----------



## MikeHag (Mar 13, 2011)

Yup... makes no sense to me, 9 bar is 9 bar. Not sure what capacity has to do with it. But I'm a bit of an engineering philistine tbh. Maybe SeaChief knows...


----------



## jimbow (Oct 13, 2011)

I seem to recall reading something similar a while back. If I remember correctly it has something to do with the fact that a vibe pump creates variable pressure (it looks like an oscillating wave if graphed) and the rated pressure is actually the average (or sometimes maximum) and the actual water pressure can be +/- a couple of bar at any point in time. The OPV is designed to flatten out the top of the wave i.e. stop the pressure hitting the grounds exceeding a certain threshold.


----------



## garydyke1 (Mar 9, 2011)

I set mine to 9.75-10BAR anyway & let my grind determine anything below.


----------



## contrary (Feb 2, 2012)

They are just talking over it. Without using gauges it is quite pointless.


----------



## RobD (May 2, 2012)

9 bar is 9 bar and increasing the pump pressure to 11 bar will not increase the volumetric efficiency of a pump, that is down to the basic pump design, a vibrating pump is a two stage piston pump and its volume is limited to the oscillating frequency of the coil and the chamber sizes but will have a limit that its internal valving can operate at, an off centre rotor vane pump can be controlled but varying the motor speed and this changes both the pressure & volume capacity at the same time and when a pressure valve is fitted this will determine the pressure. but is not as effective a variable geometry pump, the man at Bezzera is talking nonsense!!

sorry rant over but as an engineer i do hate misinformation.


----------



## nobrob (May 4, 2012)

Please correct me if I'm wrong, the point the man in the video is trying to make is this:

The big machine he's talking about holds water in the boiler at 9 BAR, ready to go, so what the shower will see is exactly that.

The smaller machine uses a single pump to *pull* water from the reservoir and then *push* into the boiler. Part of the pressure is being lost by *pulling* the water, so what is *pushed* into the boiler will be less than the pump's rated pressure capacity.

For example, if the pump is rated at 15 BAR, but you spend 6 BAR pulling water up from the reservoir, voila - you've got yourself the golden 9 BARs. The question is: how hard can it really be to pull water three inches up a tube?

I think where the problem lies is that the *rated* pressure needs to be higher than the required pressure. But if you're measuring the *real* pressure in the boiler, then carry on!


----------



## RobD (May 2, 2012)

nobrob said:


> Please correct me if I'm wrong, the point the man in the video is trying to make is this:
> 
> The big machine he's talking about holds water in the boiler at 9 BAR, ready to go, so what the shower will see is exactly that.
> 
> ...


Neither of the pumps has to pull any water as most water tanks are at the same level as the pump and head, and the mains fed units have around 1.5/3.5bar pressure from the water supply, and you don't lose pressure to draw water you need to create a vacuum!! the boiler pressure is only 1.5bar and this is the steam pressure, if you had a boiler at 9 bar it would have to be much stronger to withhold the pressure, both pumps are used for the same purpose of pushing water through the coffee the only real difference is the volume the different designs can pump.

the up side for a vibe pump is that if it runs dry it does no real damage but if a rotary pump runs dry it will wear the tips of the blades inside. the down side is they are noisy,

the man From Bezzera was trying to say the the vibe pump was inferior for pressure when its mainly inferior for volume, simples


----------



## EUG (May 15, 2012)

I have watched the video and it states clearly that the boiler is at 1.1bar and not 9 bar.

However I believe the video is incorrect because the group head injector is the same size no matter what pump is fitted and providing the pump can deliver 1 shot in 25 seconds at 9 bar there is no discussion.

Put simply you can have 9 bar in a small pipe and you can have 9 bar in a large pipe, however as flow depends on the pipe size and not pressure, the flow should be the same on both pumps at the group head because the injector size is the same.

Maybe I'm wrong but there you are.


----------

