I dont have the pressure regulator install. Just direct from filter and to the pump by using 1/4" pipe.
The pressue is 2 bar after the filter which I can read from Water Pressure Gauges installed beforethe pump.

The thing Is that you should keep in mind that with fluids like water pressure is not the same as flow because a fluid is incompressible, two drops added to a fluid in a tight container can make the pressure gomskyhigh....water pressure can be 2 bar yet if the pipes are too narrow you still end up with insufficient water flowing to pump which then creates vacuum causing vapour bubbles to form which then implode...NOT good at all for your pump.

A solution was already shown by Dan, another would be to install pipes with a bigger diameter, 3/8 is likely too small and every bend, connector and other angle adds to the resistance of the pipes and to the problem..

I concur with Marcelnl on this, it is the same reason why flow control and pressure profiling aren't exactly the same thing. : )

jdrock wrote:Then it comes to my question why the pump is smoother when using tank?
When using tank it has no pressure to the pump. The pump will "sucks" the water when needed.
Even with my low line pressure after the filteration, it still has minimum 0.5-1 bar of water direct to the pump.

The problem is resistance to the "sucking". The 1/4" fluid path has insufficient maximum volume flow per second to maintain full flow to the pump. So your pump is starving for input and pulling against too much resistance. Try drinking a glass of water quickly through a cocktail straw and you'll know what you're asking your pump to do. There's much less resistance in the tank connection - it's shorter and has a larger orifice.

Unless you find a problem in one or more of the existing components in your 1/4" feed, best solution is to go to 3/8". Your boiler is a lot bigger than that in most home machines and it's designed to fill quickly enough to let you make drinks in rapid succession.

Will try to convert all the 1/4 to 3/8 this weekend and share the outcome.

bluesman wrote:Unless you find a problem in one or more of the existing components in your 1/4" feed, best solution is to go to 3/8".

I don't mean any disrespect for Dan. Obviously, an accumulator will also solve the problem. I just hate adding more pieces to what should be a simple system. There don't seem to be many others having the same problem with your machine, though. It'd be interesting to know what size feed most are using - I'm pretty certain that few use accumulators.

1/4" does the job for any SB or home-sized HX I've ever seen, including my Oscar. But I'd really like to switch him to a 3/8" feed because I like the way it looks (!) - unfortunately, the inlet on the DC version is 1/4", and changing that would require custom work I can't justify. It wouldn't change the coffee or function at all. I just love the look of braided SS hose - even on our cars and washing machines.

On a related note, I know the La Marzocco Strada programming allows you to choose whether it refills the boiler via the pump or from line pressure. Since I have a filter system, I have mine setup that way to avoid cavitation during a boiler refill. It may be worth checking the GS/3 owner's manual for a similar option (probably wishful thinking, but thought I'd mention it).

Dan - In the GS/3 You can only set if the pump is on for tea. Autofill always uses the pump.

Rip out the 1/4 inch supply line and put in a 3/8 inch line, pressure regulator goes on the machine side of the filter and you should have around 3-4 bars of pressure on it. If you watch your pressure regulator gauge with the small line (provided the line is after the filter and before the machine) I bet you will see the pressure drop to 0 when the boiler fill kicks in. You are losing all your pressure due to the small supply line and the machine is sucking the air out of the water. With just the group running the flow rate is not as high so the water debit lower. You should have 3/8 from supply to machine, no 1/4 fittings anywhere. Think of it like this. You can breath through a snorkel while walking across the room but try breathing through one while you sprint a race. Just not enough supply volume at the given load.

Removed the 1/4 and replaced with 3/8. Pump runs quiet instantly.
When autofill kicked in, the pressure dropped from 4 bar to 1 bar as compared to the previous 0.
Seems like the GS3 pump is more powerful than my previous VBM Domobar.