Hi guys,

because I'm slowly finishing my programable pressure profiling system (PPP as I like to call it) I'd like change the place where the pressure is being measured. Currently the PT (pressure transducer) is connected to the 4 way junction where the water inlet is connected (it's water coming from the pump under the sink). The idea is to remove that link and hook the PT with the group via 1/16" tubing and an M4 Beswick fitting (courtesy of Nicholas).

I've ordered some 1/16" tubing and it arrived today, but I'm not sure how it should be routed inside the machine. Should I run it as low as possible (near the base of the machine), with the least amount of bends and turns, make a coiled section or simply run it however is easiest without worrying too much?

By the way for pressure upto 10bar do I need a fancy 15bar-certified copper tubing or is ordinary tubing ok? it was advertised as:

1.575mm OD, 0.787mm ID Seamless Copper tube grade C106

Great for modelling and live steam systems (so I guess it can take some pressure).

Regards,
dsc.

For those of you who may be wondering, Tom is talking about this fitting:



which was used by BradS and later me to measure brew temperature. I got ahold of a Scace device some time after installing it and realized that its accuracy varied wildly with the "base" group temperature and flush length. I ended up replacing it with a 36 gauge TC snaked across a gasket and into the group bell, which is much more accurate across different flushing lengths and different usage patterns. So, I had retired the fitting you see above, but I've always thought it's a great spot to get super-accurate pressure readings, because it's downstream of the Elektra's flow-restricting gicleur that buffers the group from the full power of the high-flow rotary pump.

Tom--you asked me to confirm the 'specs' of the part. You can find all the info you want here. It's in the mail to EricC as of yesterday, via Express Mail.

Hi Nicholas,

thanks for the info!

I will bend the tubing the same way you did on your TC:



[dry fit]

I will run it around the solenoid, inside the machine, behind the group, maybe create a small coil positioned horizontally and then connected to the PT via Swagelok's tube fittings.

Regards,
dsc.

dsc wrote:By the way for pressure upto 10bar do I need a fancy 15bar-certified copper tubing or is ordinary tubing ok? it was advertised as:

1.575mm OD, 0.787mm ID Seamless Copper tube grade C106

1. That tiny tube will easily handle 10 bar
2. Will it clog up with coffee solids after a while and cease functioning?

Hi Andy,

crap haven't thought about that, although there should be no coffee solids behind the bell, as you've got the dispersion screen, the dispersion block and a lot of tiny holes in the bell/group itself to effectively block any coffee going back up. I guess I will just have to wait and see.

Regards,
dsc.

Hmm, I've never collected water from the 3-way solenoid valve exit, but I'd guess going by how long it takes for one of those to get clogged/stuck/leaky under normal usage that the tube will probably be OK. Correct me if I am wrong, but isn't it basically true that if you're running a couple feet of 1/16" tubing and hooking it up to the pressure transducer, aren't you using air in the tube as a buffer to water under pressure? and isn't air pretty compressible? It seems like the gauge line will fill partially with water as the air compresses during brewing, and then that water will be forced out by the compressed air when the solenoid valve opens up at the end of the shot.

That's what I would guess would happen, just reasoning through it. My only real point of concern is the 90° down-facing elbow right at the exit... if anything were to get stuck, I bet that would promote it a lot more than a more gently curved line.

Fortunately there's no real potential for harm here (other than, perhaps, your profiling system shooting the pressure up really high due to a low reading), so it'll be interesting to find out from your firsthand experience, Tom.

Hi Nicholas,

the PPP system is not going to have feedback (at least not at the moment) as it uses only the valve position info to drive the valve. This means that even if the tube gets clogged the valve will continue to operate as normal, never raising the pressure above 8.5bar. The PT will be there simply to check what's going and whether my calculations were correct or not (and to calibrate the valve min/max positions).

As you say testing it with all the elements in place will be the best way to check our assumptions.

Regards,
dsc.

dsc wrote:there should be no coffee solids behind the bell, as you've got the dispersion screen, the dispersion block and a lot of tiny holes in the bell/group itself to effectively block any coffee going back up.

I see what you're saying, but of course some solids make it back up, or periodic backflushing would not be necessary....

shadowfax wrote:isn't it basically true that if you're running a couple feet of 1/16" tubing and hooking it up to the pressure transducer, aren't you using air in the tube as a buffer to water under pressure? and isn't air pretty compressible? It seems like the gauge line will fill partially with water as the air compresses during brewing, and then that water will be forced out by the compressed air when the solenoid valve opens up at the end of the shot.

A tiny amount of that air will dissolve in the water each cycle, so the quantity of air will slowly decrease. Despite that, the pressure measurement will probably be just fine for a long time. I guess Tom will see soon enough.

Hi guys,

well it looks like it might take a while to connect everything, even though I'll have the Beswick group fitting tomorrow. The reason for this is the 1/4" BSP thread on the PT which apparently is something out of this world (at least to Swagelok). There's no 1/4" BSP to 1/16" tubing adapter available of the shelf and to make one I'd have to buy 3 parts which might not fit under the PT:

- 1/4"BSP to 1/4"NPT adaptor

- 1/4"NPT to 1/4" tube fitting

- 1/4" tube to 1/16" tube adaptor

To make things worse they don't make the BSP- NPT adaptors in brass which means they cost more then the two other parts together (which are brass).

I guess I'll put this on hold for now as it looks and sounds awfully annoying and overcomplicated.

Regards,
dsc.

Perhaps you could get a skilled machinist to braze them together? Or to braze them into a chunk of brass?

Mark