Expansion value and pressure setting help

[mswanson]

Hi,

I noticed some funny sound coming from the group when pulling shots. So after searching the forum, it seemed the first step would be to clean the expansion valve. I took it apart, and sure enough there was some stuff that needed to be cleaned out. The sound seems to be gone.:)

Question 1. When replacing the expansion valve, the spring faces towards the counter, correct? The rubber disk on the spring should face upward?

After fighting it back in, (I hope I put it together correctly), I went about resetting it's setting. I ran the group pressure up to 12.5 (it was set at 9 bar). I put the backflush disk in.

Question 2. When i pull a shot I do not notice any water coming from the tube next to the expansion valve until after the shot is over. Should water be coming before the shot is over? How long should I let the pump be at 12.5 bar (it's in the red)?

Question 3. When resetting back to 9 bar for normal operation, should that be measured at the peak pressure throughout the shot?

I'm alittle nervous when using this backflush disk and how long the pump should run when testing/backflushing...

Thanks for any help.

[Zarzicki]

When I pull a shot, if I tamp and grind it correctly, the pressure will remain at 9.

When I backflush, I usually count to about 10 and then press the DBL shot button again to stop the backflush and that will open the 3 way valve with water exiting into the drippan.

hoped that helped a little. Zarzicki

[chas]

Hi,

I noticed some funny sound coming from the group when pulling shots. So after searching the forum, it seemed the first step would be to clean the expansion valve. I took it apart, and sure enough there was some stuff that needed to be cleaned out. The sound seems to be gone.:)

Question 1. When replacing the expansion valve, the spring faces towards the counter, correct? The rubber disk on the spring should face upward?

After fighting it back in, (I hope I put it together correctly), I went about resetting it's setting. I ran the group pressure up to 12.5 (it was set at 9 bar). I put the backflush disk in.

In the future, it is MUCH easier to get the expansion valve started when replacing it, if you remove the drip tray and then use a metric deep socket. You can then easily push up on the bottom of the socket with one hand while twisting the expansion valve with the other.

Question 2. When i pull a shot I do not notice any water coming from the tube next to the expansion valve until after the shot is over. Should water be coming before the shot is over? How long should I let the pump be at 12.5 bar (it's in the red)?

This expansion valve design has always left me scratching my head. You set it to start opening around 12.5bar. Yet sometimes it drips when the group boiler is running such as right after a shot when there is no pressure on the valve at all. There is a lot of machine-to-machine variance in this area but most of them do this to dome degree.

Once you have replaced the expansion valve you insert the rubber disk or a blind basket and adjust the group pressure to 12.5bar. Then you twist the expansion valve in whichever direction is required so that the expansion valve just starts to drip at 12.5bar. Then you adjust the group pressure back to 9bar or whatever you want your running group pressure to be. It won't hurt anything to run the machine at 12.5bar during this process. I just wouldn't leave it running and go off for a smoke break!

Question 3. When resetting back to 9 bar for normal operation, should that be measured at the peak pressure throughout the shot?

I'm a little nervous when using this backflush disk and how long the pump should run when testing/backflushing...

Thanks for any help.

The rotary pump has a built-in pressure bypass valve. (Actually the V2 Mini also has a pressure bypass valve, a rarity for vibe pump machines.) Should that fail, that's what the expansion valve is there to protect you from. It's not like most of the vibe pump HX machines where the pump will actual choke and labor if left running with a blind basket installed.

[bgour]

The rotary pump has a built-in pressure bypass valve. (Actually the V2 Mini also has a pressure bypass valve, a rarity for vibe pump machines.) Should that fail, that's what the expansion valve is there to protect you from. It's not like most of the vibe pump HX machines where the pump will actual choke and labor if left running with a blind basket installed.

I've noticed odd behaviour on my S1 V1 during a backflush: the pressure rises quickly to ~125psi and stays there (all good). But then sometimes after a few seconds at 125psi it continues upwards until 180 and stops. I presume it's hitting the expansion valve limit of 12.5 bar, but why is it getting that high in the first place? Could it be due to failure of the pump's "built-in pressure bypass valve" as mentioned above? Should I be concerned about this or is it "normal" during a backflush?

This is measured with a portafilter gauge. My line pressure is 25 psi (behaviour was identical when my line pressure was at an unregulated 58 psi).

[chas]

I'm not sure I can explain it, but it's normal behavior with a PF Pressure Gauge. If you remove the PF and run a shot into the blind basket to fill it up, lock in the PF, then run another shot this behavior is less likely to happen than if you lock in the PF filled with air.

So it seems like maybe the air is getting superheated and expanding to increase the pressure. The group pressure gauge picks off right at the pump whereas the PF pressure gauge is right at the group. All things being equal when using a blind basket, both gauges should read the same. However, the trapped air appears to change the equation at the group.

BTW: Now that I have a GS/3, I purchased a Scace II which has a PF pressure gauge built in. The main difference between this device and closed PF pressure gauge is that the Scace II has a small pinhole in the end which lets through water at the same rate as a properly tamped puck. I discovered that the pressure runs 0.7bar lower at the group than is indicated by the built-in group pressure gauge. To be sure the Scace was accurate, I temporarily plugged the hole. After that the Scace II was in perfect agreement with the built-in group pressure gauge.

[bgour]

I'm not sure I can explain it, but it's normal behavior with a PF Pressure Gauge. If you remove the PF and run a shot into the blind basket to fill it up, lock in the PF, then run another shot this behavior is less likely to happen than if you lock in the PF filled with air.

So it seems like maybe the air is getting superheated and expanding to increase the pressure. The group pressure gauge picks off right at the pump whereas the PF pressure gauge is right at the group. All things being equal when using a blind basket, both gauges should read the same. However, the trapped air appears to change the equation at the group.

Thanks chas, that exactly explains the behaviour I'm seeing.

BTW: Now that I have a GS/3, I purchased a Scace II which has a PF pressure gauge built in. The main difference between this device and closed PF pressure gauge is that the Scace II has a small pinhole in the end which lets through water at the same rate as a properly tamped puck. I discovered that the pressure runs 0.7bar lower at the group than is indicated by the built-in group pressure gauge. To be sure the Scace was accurate, I temporarily plugged the hole. After that the Scace II was in perfect agreement with the built-in group pressure gauge.

0.7bar sounds about right and if so then I'm running barely 8 bar at the puck. Might be worth bumping a bit.

[JohnB]

I had the same thing happen with the P/F gauge I bought from Chas. Sometimes it does it, some times it doesn't. I'm going to modify it to work like the one Bob built: http://www.home-barista.com/espresso-ma ... .html#1012

[JohnB]

I went to Lowes today & got the pieces required to add a flow valve to my p/f pressure gauge. Setting it to flow 2 ozs in 25-30 seconds I really didn't see much of any difference between the S1 group pressure gauge & the p/f gauge. It is nice not to have the pressure creep up on the p/f gauge so it was worth the time/$$. I'll play with it more tomorrow to try to mimic my longer/lower volume shots & see how the pressure looks.