Hi everyone. I'm having a problem with my NS Mac Digit. Several weeks ago, while pulling a shot it would open up and release water to the drain. I found that the water was coming from the Neplax (expansion) valve and not the three way valve. But the valve would stick open, running water straight through the machine and out the drain.

I replaced the spring and the viton bushing and I soaked the valve in vinegar to remove scale. After putting it back together I had a couple great pulls. But the water started leaking after that first session. Now, all pulls are giving me about 1/2 volume in the cup, and half in the drain.

I'm not sure why the valve body itself is faulty, but apparently replacing the "guts" didn't do it. Should I be looking elsewhere for the problem or just replace the entire valve? There is a double gauge on the machine, but the brew pressure gauge is broken and always reads around 10 bar.

Thanks!

Then you need to replace the gauge in order to set the expansion valve correctly as a FIRST step.

See this: http://www.nuovadistribution.com/older_models.html

Thanks for the reply. The neplax valve on this machine is non-adjustable. The original version is fixed at 9 bar and the newer version opens around 16 bar (so I've read on these boards). That's why I thought replacing the spring would increase the resistance. But now I wonder if the entire valve needs to be replaced to get 16 bar resistance.

I refurbished the machine about 1 year ago and replaced the gauge at that time. Using that gauge I set the pump pressure at 9 bar. I'm not sure if it is coincidence that the pressure gauge went again or something else. I took the gauge out thinking there could be a blockage in the line but the needle just sits at about 10 bar.

Maybe my pump is set for a little more than 9 bar and opening up the neplax valve? I suppose I should test pressure at the group.

Replace the gauge and the neplax?

Deferring to any specific instructions that NS might have on this machine, it would be correct to supply the rotary pump with 35 psi (~2.5 bar) of quality water and adjust the pump to produce 9.0 bar.

When I look at the parts book, I see two expansion valves - one at the group and the other at one of the drip tray illustrations. Which one is yours?

Typically thermal expansion valves are set to drip . . . drip . . . drip at 11-12 bar but if the valve is non-adjustable then I would make sure it drips at whatever pressure it is supposed to. Yes, there's small pressure losses through the hydraulic circuit when you are flowing water but to have a valve set at 9.0 bar seems low to me.

My machine has the valve at the back of the group head. When the problem first started, water was streaming out of the valve because the retaining piston was "stuck crooked" so it could not re-seat. I thought maybe some scale was causing that piston to stick. My first one or two shots with the new spring and gasket were great. Full volume, great crema, and the machine just sounded quieter. But then the problem started again and put me back where I started ... further back actually. There is more coming out the neplax valve now than there was before the new parts.

Now that the pressure gauge is dead I can't tell you what the water pressure is, but I'm pretty certain is was around 2-3 bar. I originally set the pump output pressure to 9 bar. It does seem that 9 bar neplax is too light. Maybe that's why the new version is 16 bar.

I guess I will have to get another gauge and get some readings. Perhaps the pump pressure adjustment screw was not adequately locked and pressure has gradually increased to 10+ bar, causing the neplax to open during each and every pull. Even so, I think I'd like one of those new neplax valves that open at 16 bar, or an adjustable OPV.

That's not necessary (installing an OPV).

That valve is a thermal expansion valve designed to go drip . . . drip . . . drip - NOT to regulate pressure. I would take the valve apart and make sure there is nothing holding it open.

Thanks again for the tips. I have a new gauge on the way so I can start with setting the pump pressure to 9 bar. One of the tech's at Nuova Simonelli told me this Neplax opens at 12 bar. Maybe my pump is set too high. Now that I've de-scaled the valve body the sticky valve piston seems to have gone away.

I'll post an update when the gauge arrives (next Monday). As long as I was ordering the gauge I also ordered a bottomless portafilter. I just hope my shots look as good with the bottomless as I "think they do now".

Are you feeding this machine with filtered/treated pressure regulated water?

Whether yes or no, I would turn the pump pressure adjustment out (counterclockwise) at least one full turn before installing any gage. The expansion valve should behave as indicated at ~12.0 bar and then set the pump to ~9.0 bar with a blind filter.

Good call Eric! I looked inside at the pump and guess what I saw? The lock nut was way down at the bottom of the adjustment screw. So I backed out the screw one full turn and locked it. I'm drinking a great espresso now that pulled nice and slow but didn't blow any water out the neplax at all! Yay!

I am not filtering my water, which may be the reason I ruined this gauge. Probably some debris found it's way into the gauge and blocked it. So the first thing I'll do before installing the gauge will be to install a filter. Then I will purge water through the gauge capillary line to make sure there is no particles or sediment.

I think we might have nailed this one down. Good thing, my brother-in-law is in town and he always looks forward to espresso drinks at our house! Now to order some fresh beans. A friend of mine used to be a roast master before her current life as a lawyer. She said Wegmans (for those of you in the Northeast US) French Roast is great for espresso and it is usually very fresh. Anyone from around here care to comment? Concur or disagree?

Thanks for your help!
Ted