Reducing your water pressure for an espresso machine
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All plumbed espresso machines require water within certain pressure limits, these can vary between makes of machines, but it's generally beteen around 1.5 to 2.5 bar. As always check with your manufacturer if unsure. Water pressure regulators, usually consists of an easy fit self sealing connector and water pressure gauge with adjustment on the body of the device. A pressure-reducing valve acts as a buffer between the high water pressure supply and Espresso machine, mains water pressure is reduced to the safe required level during flow or non flow conditions. Also called water pressure reducing valves they are compact, inexpensive regulators performing an important function:
Automatically reduce and “regulate" (by maintaining your pre-set pressure), the high incoming water pressure from the water mains to provide a safe, more moderate, but satisfactory functional pressure for the espresso machine.
Note: They will not increase mains pressure that is already too low, they can only reduce it as required.
The pressure regulator usually needs to maintain the pressure at around 1.5-2 bar from your mains water supply For Rotary pumps this level of pressure ensures that the pump does not cavitate (and get damaged) through water starvation.To much pressure and the pumps balanced bypass is defeated and cannot successfully regulate it also has "less room for manoeuvre", in addition there is the extra pressure placed on everything else within the machine…..so a slightly leaky solenoid valve might prove to be more of a problem than it otherwise would be. For Vibration pumps with mains connection there are similar issues and pressure should be regulated in the same way. If a tap on the water circuit is opened, the pressure regulator will increase pressure as needed to again ensure the pump does not run short of water (subject to the maximum mains water pressure available and the flow rate being demanded.
It is a common misconception that closing a ordinary ball type valve to limit the flow to the espresso machine will perform the same function, but it will not. Although the pressure might appear low with a modest flow rate, the second the water stops flowing or flows more slowly(e.g. the espresso machine is no longer pulling a shot), the pressure will quickly rise to the maximum mains pressure (which could be as much as 4 or 5 bar! or 70 psi). You may think well so what, but again the relatively low flow of the espresso shot….only 30 ml in 25 seconds, will most likely leave the machine subject to 5 bar during the shot as well. The reason I make this point is there is no real substitute for a proper pressure reducing valve and all plumbed in machines should have them (especially as the majority will include a 1 way check valve).
The only situation where it may not be desirable is if your water pressure is already only 1.5 bar, does not go higher and in this case water pressure reducing valve might lower the pressure slightly too much as there is usually some extra restriction to the water flow due to their design.
The operation of a greatly simplified valve is shown below
It works on the basic principle that dynamic pressure and flow are closely related and not individual properties. Static pressure is a different thing, you can have a static pressure of 2,000 bar in an enclosed vessel, with a max possible inlet flow rate of 1ml per minute….the moment a flow of liquid from the pressure vessel exceeds 1ml per minute, the pressure will drop to zero within the Vessel.
Such devices can be obtained from plumbing shops or many coffee machine retailers