High pressure pump and method for compressing a fluid

1. A high pressure pump comprising:

a compression chamber having an inlet for connecting to a fluid supply to intake a fluid, and an outlet;

an inlet check valve between the compression chamber and the inlet;

a digital inlet valve between the compression chamber and the inlet check valve;

a variable volume chamber connected to the compression chamber through a manifold and the digital inlet valve; and

a plunger or piston configured to compress the fluid in the compression chamber and the variable volume chamber, wherein a bottom part of the plunger or piston is integrated into a bottom part of the variable volume chamber such that the bottom part of the variable volume chamber moves together with the bottom part of the plunger or piston;

wherein the variable volume chamber comprises a bellows integrated into the bottom part of the variable volume chamber and the bottom part of the plunger or piston; and

wherein the high pressure pump further comprises a line directly connecting the compression chamber with the variable volume chamber or the manifold, and a safety valve selectively opening or closing the line to prevent overboost in the compression chamber.

2. The pump of claim 1 , wherein the bellows is made of a metal or a plastic material.

3. The pump according to claim 1 , wherein the manifold comprises a conduit, the conduit having a first end fluidically connected to the variable volume chamber and a second end fluidically connected between the inlet check valve and the digital inlet valve.

4. The pump according to claim 1 , wherein the manifold comprises at least two separate conduits.

5. The pump according to claim 1 , further comprising a control unit to provide electrical control of the digital inlet valve.