So, I could not contain myself and went ahead with the 3rd stage modification. I was able to source a BRAND NEW motor from ebay for $25, and a pump directly from Fluid-o-Tech for $66. With shipping costs and whatever valve/fittings added, the whole setup is only around $120 or so. Quite a deal!!
To keep a "reasonable" pre-infusion, I installed a needle valve downstream of the pump. With it barely crack open, I was able to get down to about 90ml of unrestricted flow in 10 sec. When testing with a blind filter, it takes about 6 seconds to ramp up to full pressure (of 9 bars), which is comparable to the original vibe-pump setup. Interestingly, the pressure with no restriction is now only about 6 bars as opposed to 9 with full restriction.
The pump bypass water @ line pressure from inlet to outlet when not operating, and the vanes do not provide a seal from inlet to outlet. This, in conjuction of keeping my old vibe-pump plumbing (more specifically, the OPV valve), cause water to flow to my drip tray constantly. To remedy this situation, the solenoid from the old direct connect kit was recycled and put on the outlet of the pump. Water is now only allow to flow when the motor turns on.
The pressure drop caused by the constant heating element on/off (due to PID) also went away with the rotary pump conversion. This is the main reason for the upgrade and I am look forward to see what difference it makes.
The machine sounds very differently now when pulling a shot. A bit errie actually with the high pitch whirling of the rotary pump instead of the violent rattle of the vibe that I am used to. I think I will really enjoy the quitness and the steady brew pressure.
[UPDATE 5/26/2006]
OK, I managed to get some free time and finally pulled some shots from the new setup. Either the coffee I am using is getting a bit old (Ecco Daterra Reserve, roasted 5/11), or new rotary pump is really giving that smoothness I been seeking from my home shots. The shots are 1.5 oz double pulled at around 199/200F with a aftermarket ridgeless double (~18g dose). It was loosing a bit of the flavor intensity, but still quite tastey. Most importantly, I was able to capture that silky smoothness I got from LM shots at Simon's that I was never able to reproduce at home. To me, the really steady brew pressure took out all the graininess and rough edges of the shot. I know there were two previous study done by Jim Schulman and Ken Fox that showed no difference between vibe and rotary, but it did made a positive impact on my setup. A totally worthy upgrade! I am excited to try some fresh coffee on the setup to see if I get that clarity in the cup.
-Ben
