Posted Tue Aug 30, 2011, 11:20am Subject: Silvia pressure oscillating
Hi. I have a modded Silvia v1 and was hoping to get some help debugging. I have installed a oil-filled pressure gauge (via a t connector splitting off right after the pump before the teflon tube that leads to the OPV) and when brewing it shows the pressure osciallating up and down from about 8 bar to 9.5 bar. The movement is very rapid -- likely occurring with each vibe cycle -- so you just see a grey blur as the needle moves. When I shut off, the pressure stays at about 8 bar but then after about 30 seconds will very gradually creep back to about 4 bar. I tried descaling, then disassembling/cleaning both the OPV and the pump on the assumption that either the OPV getting stuck and opening too slowly or the pump leaking pressure back during the downstroke might be the issue. The latter seems to me now to make the most sense but before I go buy a new pump non-returnable pump, I was hoping people here might suggest any other ideas I should try. Note: if it matters, the OPV is the older v1 style that is only adjustable by adding copper washers and I have 2 such washers on it. Also note: I haven't seen any dripping into the pan during brew so I don't think it is the solenoid leaking but maybe I'm wrong about that.
I have a harebrain idea about this, but havent reduced it to practice as yet. What if one were to get a second pump, connect the inlets and outlets together, then connect the coils out of phase with each other. This shoud create a 2 "cylinder" pump. The pulsations will be at twice the rate and lower in amplitude. If that's not good enough you can shift the phase of the power 90 degrees with a capacitor get yet two more vibe pumps and have a 4 "cylinder" pump. I have to believe this is cheaper than a rotary pump.
This is not unique to your system. One solution is to add an air bottle in the circuit that will act as a damper and reduce the pulses. This could be a small propane cylinder ( after cleanup) with mechanical mod. Just a suggestion never tried Mark
I wondered about this but the guy I bought the gauge kit from also has his installed on a Silvia and he said his pulsations aren't nearly as large so we wondered if it was a symptom of an actual. One possibility is his has the newer style OPV valve so perhaps that responds quicker to the pulsing or something and makes the amplitude smaller. Anyone else with a gauge'd Silvia (or, I suppose, just a gauged Ulka pump model) that can weigh in on how wide the fluctuations are during brew?
On the damping idea... I had thought of this, too. Basically you want a mechanical low pass filter so either an air chamber (a pressure "capacitor") or a something like a flywheel (an "inductor") could help. Does the pre-infusion chamber on E61 machines effectively do the same thing? I've wondered if that is some of the benefit since one one think it would break up the puck to have the pressure moving up and down aggressively.
They sell things as hardware stores that are supposed to eliminate knocking pipes which are basically air chambers. I wonder if one could use one of those. The trouble might be getting the size right. You don't want to have to wait a minute for pressure to build up.
What you're looking for ideally would be a 'wet' or liquid filled gauge that dampens the ocillations. Failing that, what is called a 'snubber' valve in line on the dry gauge.
Pressure snubbers use a capillary orifice to smooth out line pulsation and surges without the use of any moving parts. Snubbing action is fixed and automatic.
Snubbers prevent the meter seeing the pressure oscillation . But the "pressure Capacitor will dampen the oscillation in the pressure and will minimize the effect of pressure oscillation in the espresso process oscillation. An optimization is needed as you point out the filling time. The pre infusion time could be adjusted to include the (capacitor) filling time At some point all these discussions will be academic one may not have an appreciable effect on the espresso brewed.
That's what's weird.... my gauge *is* oil filled. (it is a Wika branded gauge). So either the oil isn't sufficiently viscous or the pressure changes it is seeing are greater than the ones other gauges see from these pumps.
Symbols: = New Posts since your last visit = No New Posts since last visit = Newest post
Forum Rules: No profanity, illegal acts or personal attacks will be tolerated in these discussion boards. No commercial posting of any nature will be tolerated; only private sales by private individuals, in the "Buy and Sell" forum. No cross posting allowed - do not post your topic to more than one forum, nor repost a topic to the same forum. Who Can Read The Forum? Anyone can read posts in these discussion boards. Who Can Post New Topics? Any registered CoffeeGeek member can post new topics. Who Can Post Replies? Any registered CoffeeGeek member can post replies. Can Photos be posted? Anyone can post photos in their new topics or replies. Who can change or delete posts? Any CoffeeGeek member can edit their own posts. Only moderators can delete posts. Probationary Period: If you are a new signup for CoffeeGeek, you cannot promote, endorse, criticise or otherwise post an unsolicited endorsement for any company, product or service in your first five postings.
= No New Posts since last visit 