shadowfax wrote:I thought they said they were using 13mm gears (I have reached out to them to confirm), and that it is custom pump setup from Fluid-o-Tech. The gear size was one of the things (as well as mounting and inlet hose) that they worked directly with Fluid-o-Tech to resolve.

I confirmed with Jason just now. They did, in fact, settle on the 9mm gears; so I was incorrect about the 13mm gears.

Eric Svendson sent me some data on the 4 mm vs. the 9mm, and it appears that the main difference is the flow that they deliver at the same pressure and pump speed. He seemed to think that they might have selected this pump to deliver a high flow rate for steam boiler auto-fill. But I am thinking that, if I understand correctly, selecting the gears that deliver a higher flow rate at a lower pump speed (assuming a fixed pressure in the ~9 bar range) allows them to run the pump at a lower speed, where it will make considerably less noise. The consequence of doing this is probably that you can't use the minimum pump speed (~200rpm, I think) to deliver a tiny flow rate to the group like you can with the 4mm gears, but Slayer isn't doing this-they use the needle valve to restrict the flow rate.

For me, one of the most intriguing design features of this machine is the pressure transducer port in the custom fitting between the 3-way and the group. That's the perfect place to measure pressure at the puck. Oh, how I wish my GS/3 had a port like that!

I can see this wasn't an easy thing to do -- the fitting appears to be custom-made and is welded to the group. I have no doubt that this is the best approach. Unfortunately, the idea won't translate to my GS/3. I've tried to dream up ways to add a true group pressure port to it and don't think it can be done without a radical, difficult, ugly and possibly dangerous mod to the TL-30 tube and stainless group.

shadowfax wrote:I The consequence of doing this is probably that you can't use the minimum pump speed (~200rpm, I think) to deliver a tiny flow rate to the group like you can with the 4mm gears, but Slayer isn't doing this-they use the needle valve to restrict the flow rate.

I have the 4mm pump on my GS/3, and from a practical standpoint I don't think 200 rpm capability has much value, especially if there's any line pressure.

When I use your low-line pressure pre-infusion technique and then slowly bring the pump up to speed, it's hard to keep the initial rpm under 400 rpm, and most of the time it jumps to about 1000 rpm. The flow rate is still quite slow at that speed. Pressure is probably on the order of 3 BAR or less. I would need a pot with much more travel to reliably set the speed under 1000 rpm, and I think that probably would involve an impractical wire-wound pot. It might be doable with the speed voltage under microprocessor control, but I'm not setup to try that (yet.)

I think Slayer made the right choice with the needle valve. Without it, low rpm might have some value with a reservoir, but you'd still need a way to more precisely control the speed voltage to the pump.

Peppersass wrote: That's the perfect place to measure pressure at the puck. Oh, how I wish my GS/3 had a port like that!

Where do they take the pressure reading on the GS3?

On the original (automatic) GS3, it's just on the side of the boiler, i.e. upstream of the 0.6mm gicleur. So, the pressure can potentially read higher than the pressure downstream of the gicleur. The Slayer V3 group measures "on" the pickup tube, which reads at least nearly identically to what a Scace 2 would read.

GS3 (automatic): GS3 (paddle group): Slayer (V3 group)

Peppersass wrote:For me, one of the most intriguing design features of this machine is the pressure transducer port in the custom fitting between the 3-way and the group. That's the perfect place to measure pressure at the puck. Oh, how I wish my GS/3 had a port like that!

I can see this wasn't an easy thing to do -- the fitting appears to be custom-made and is welded to the group. I have no doubt that this is the best approach. Unfortunately, the idea won't translate to my GS/3. I've tried to dream up ways to add a true group pressure port to it and don't think it can be done without a radical, difficult, ugly and possibly dangerous mod to the TL-30 tube and stainless group.

That is a super easy task on the Synesso, just sandwich the port between the 3 way and the flange on the group.
I have found that sometimes it helps to pressurize the boiler before I open the 3 way, this allows the pump to get running and stabilized before I open the port, then I am only dealing with a transient pressure abberation that the pump is better positioned to deal with because it is already running.
This is useful when I pre-infuse with very low pressures (1-2 psi)

1. pressurize the boiler and allow to stabilize (all the blips and spikes from startup don't matter if you aren't brewing)
2. close the group orifice down to near 0
3. open the 3 way
4. slowly open the group orifice to standard (0.6mm)

system is stable and no big pressure spikes on the puck from pump startup.



Sean

The Speedster reads right at the base of the 3 way where the pickup tube enters & exits to the group outlet. Definitely downstream of the Gicleur which is now located back in the HX to boiler feed pipe. I still see higher readings on the pressure gauge then what I get using a p/f pressure rig.

John, are you sure about that? I thought the Speedster just had its pressure gauge connected to the boiler on the side. I don't have a picture, though, and I can't remember for sure. I found this picture of a Spirit that I took at SCAA last year, and it definitely reads brew pressure from the side of the boiler. Sorry in advance for the low image quality. See:


Pressure gauge appears to be connected to the fitting on the left side with the capillary tube going out of it.

So the Speedster is different?

Just checked. It's the pre infusion chamber take off coming off the bottom of the 3 way. My bad! Pressure gauge take off is as your photo of the Spirit shows. Still down stream of the Gicleur though! Haven't checked to see if the reading is more accurate since moving the gicleur back into the HX feed pipe???

I forgot that it got moved on the Speedster from the pickup tube to the HX outlet. I'd bet that makes it about as accurate reading from the side of the brew boiler side as reading from right by the 3-way junction on the Slayer. That might be a good modification for a pressure profiling GS3 as well.