Home built pressure measuring rig

[simonp]

Here is a quick summary of something Matts and I have beem working on. It's a rig for checking your pump pressure at the brewhead. The Silvia portafilter has a notch in the rim under the basket which means you can't get pressure in the portafilter body, so, you cannot mount a pressure gauge. Pressure measuring portafilters ar quite pricey, and not easy to get. We decided to use a method Matt saw somewhere about using a blind filter basket.
Basically we made a hole in the centre of the blind basket and mounted a very small pneumatic fitting which would fit inside the portafilter, and seal to the basket. This fitting has a push-fit connection for flexible plastic pipe. We then threaded some platic pipe through the spout and the portafilter and connected it to the fitting. Then the portafilter is locked in as usual. On the other end of the pipe is another push-fit connection which is screwed on to a glycerine filled (damps quick pressure changes) 14 bar pressure gauge.
Once it was all fitted I hit the brew switch, and watched the pressure rise. It got to 10 bar and BANG , off came the pipe in the portafilter! It seems the basket deforms slightly under pressure which pushed the fitting against the bottom of the portafilter and released the pipe, Matt did not have this problem. No problem, I tapped the fitting to deform the basket slightly towards the showerscreen.
I then re-connected, and hit the brew switch again. Success up the gauges went to 12bar and stayed. I did get a tiny leak of water, but that was from the grouphead seal, so I think it needs a good clean.
So, the Silvia can run up to 12bar, not good for doing ristrettos. Next plan, how to adjust the over pressure valve, as the usual 2 gasket method makes my pressure way too low.

One, or both of us will do an article of this soon (when we have the time), but I thought some piccies would interest people.

[mnemonix]

Cool !

Might a reinforced or braided hose be better for this application to reduce deformation or is it not necessary at these pressures ?

Chris.

[kingseven]

Why didn't they teach me THIS on Blue Peter?

[simonp]

Might a reinforced or braided hose be better for this application to reduce deformation or is it not necessary at these pressures ?

Nah, the pipe is good for at least 25bar.

[simonp]

Why didn't they teach me THIS on Blue Peter?

There was no sticky back plastic involved, so no good for Lesley Pete & John (my era presenters)

[Ian]

Wouldn't it have been easier/cheaper to borrow Eric's pressure gauged pf?

I did the pressure mod. thing a while back and didn't like the result so put it back to standard. Of course, I have no idea what the pressures were before and after the mod. It would be more interesting and objective if you adjusted the pressure relief valve to where it suits your taste buds then measuring what the pressure is.

You could use a thicker copper washer and anneal it to make it soft then you can make it thinner by hammering it or graunching it up under the bolt. When it work hardens, just re-anneal.

Nice looking gauge, did you get it online and do they do a panel mount version?

Ian

[simonp]

Wouldn't it have been easier/cheaper to borrow Eric's pressure gauged pf?

I posted a forum message to see if anyone had a gauged PF, but got no positive replies, also I'm not sure which PFs fit a Silvia, I know not all 58mm ones will.

The rig was about £23 including a (a little pricey) Rancilio blind basket.
The pneumatics came from this bunch http://www.airlines-pneumatics.co.uk/. The gauge was £8.83 +VAT, and there is a panel mounts bracket for them for £2.39.
I have toyed with moving the OPV from the boiler, and putting a pipe in so I can 'T' in and put a brew pressure gauge in the Silvia.

My plan with the pressure adjustment is to add the second washer (I too wasn't impressed with the espresso with this in), a dn then make up some very small shims for the spring to sit on and adjust the spring tension, and hence pressure this way.

[matts]

Wouldn't it have been easier/cheaper to borrow Eric's pressure gauged pf?

I did the pressure mod. thing a while back and didn't like the result so put it back to standard. Of course, I have no idea what the pressures were before and after the mod. It would be more interesting and objective if you adjusted the pressure relief valve to where it suits your taste buds then measuring what the pressure is.

The gauges were very cheap as you can see. It was a little project and a nice thing to have about the place, if you have a standard pf (ie: without the notch in the rim) you could do it for the cost of the gauge and one adapter fitting, so not much more than £10?

I did the pressure mod ages ago and never measured, I liked it more than the stock way. Measuring now, the extra gasket gave me 8 bar, the standard setup 11.5 bar. Neither of which were ideal...but 8 bar is OK. I have sanded down one of the gaskets and now have 9.25 or so.

Matt

[moccafaux]

Aint it possible that we are pushing it too far?

[simonp]

Aint it possible that we are pushing it too far?

Not really. There are HX machines that use vibe pumps that allow adjustment of the brew pressure. We are just attempting the same thing. It is just a simple way to get the Silvia closer to the espresso quality of a commercial style machine, but at little cost.
I suspect that the reason the over pressure valve is set at 12bar+ at the factory is so that if home users grind a bit too fine, or tamp too hard that you will still get a shot. Brewing at 9bar means that there is less leaway, but this not a problem for us enthusiasts.

I know some of these mods seem OTT to some, but if I can see an easy way to make the machine better, why ignore it? If I had the cash for a commericial machine with all the adjustability built in I'd have one, but I don't, so I'm using knowledge to get close on a budget

[matts]

Aint it possible that we are pushing it too far?

Making sure the pressure of your machine is correct a step too far...? I take that in the spirit with which it was intended of course

To get some perspective on 'taking it too far' check these out:

http://www.bellataiwan.com/phpBB2/viewt ... 63&start=0
http://www.bellataiwan.com/change/sv_al ... alanwu.htm

(say no to Taiwanese language support and just wait for the pics to load)

Matt

[simonp]

Now that IS taking it too far

I now have my pressure at 9.5-9.75 bar measured hot, so no more tinkering for a while :drink:

[simonp]

I've just tried a shot with the new brew pressure. I used some home roast Hasbean Espresso Blend. I got a 28 second ristretto, and boy did it look good coming out of the spouts! It dripped and hung just liek some of the Vid clips I have seen, I always found that after the frist 10 seconds the pour got quicker and paler before. This stayed much darker, and the crema in the cup is redder. It tasted good too, very smooth, and seemed less bitter.

[Ian]

I posted a forum message to see if anyone had a gauged PF, but got no positive replies, also I'm not sure which PFs fit a Silvia, I know not all 58mm ones will.

I missed that, now I come to think of it, I haven't seen Eric about for a while, I wonder what he's up to?

The rig was about £23 including a (a little pricey) Rancilio blind basket.
The pneumatics came from this bunch http://www.airlines-pneumatics.co.uk/. The gauge was £8.83 +VAT, and there is a panel mounts bracket for them for £2.39.
I have toyed with moving the OPV from the boiler, and putting a pipe in so I can 'T' in and put a brew pressure gauge in the Silvia.

The gauge was much cheaper than I expected, I see they come from a pneumatics place - Are they suitable for a permanent fitment with liquid at high temp?

My plan with the pressure adjustment is to add the second washer (I too wasn't impressed with the espresso with this in), a dn then make up some very small shims for the spring to sit on and adjust the spring tension, and hence pressure this way.

Shimming is a typical way of adjusting the oil gallery relief valve in engines and large gearboxes.

Have you thought about fitting an adjustable relief valve as per the type found on the HX machines?

Cheers

Ian

[Ian]

It was a little project...

Absolutely, a project exercises the old grey cells - I've got a list of projects that I haven't even started yet...

I did the pressure mod ages ago and never measured, I liked it more than the stock way. Measuring now, the extra gasket gave me 8 bar, the standard setup 11.5 bar. Neither of which were ideal...but 8 bar is OK. I have sanded down one of the gaskets and now have 9.25 or so.

What do you find the taste difference to be going from 8bar up to 9.25?

Cheers

Ian