Automated/Regulated Pump - Solenoid Valve or Check Valve?

GeckoSub · September 24, 2019, 9:55am

Hi Guys,
So, I am putting together a small vac pump system for bagging smaller items.

First trial run yesterday and things are OKish. Had a leak in the bag which sealed itself after 5-6 hours (I guess it happens), but until then I had to manual switch on the pump every 15-20mins.

So, now I know next, imminent, upgrade is an SMC pressure switch (ZSE30 series).
But my question is, can I get by with just using a non-return check valve instead of a solenoid valve? I thought solenoid was a must-have but then saw mentioned here, that it seems people get by without? That would be nice to keep things simpler for now.

Would that be OK?

Yeah, I need an SSR relay and 24V power too.
Pump is a small AC evacuation pump. Works nicely so far (tested in the shop and it pulled substantially higher vac than its bigger brothers).

Michiel · September 24, 2019, 11:58am

If you use the SMC switch you don’t need a valve at all, unless your pump leaks.

GeckoSub · September 24, 2019, 1:10pm

Hi Michiel,

OK, I just read that pump building manual on Joe Woodworker, and I think the reason for the Mac three-way valve (and small sub reservoir) is to protect the pump from having to start up against a hard vacuum. Supposedly, that’s not healthy for the pumps.

But since it seems I can get by without it, though maybe shorten the life of the pump a bit. For now, I’ll go with switch and check valve (not sure if pump leaks or not, I have a feeling it might). The pump is quite cheap and I need it to work kinda pronto. Then later, if I feel like it, I can upgrade with the three-way solenoid + sub reservoir.

Thanks! Off to buy SMC switch:-)

Michiel · September 24, 2019, 1:10pm

A reasonable brand vacuumpump has no problems with starting under vacuum.

GeckoSub · September 24, 2019, 11:58am

Mine is quite unreasonable;-)
(Meaning, it is the smallest AC pump I could find. Cheap and low flow, but it seems to pull a good vacuum, even better than the slightly bigger models. And I wanted a small, cheapo pump to start with.)
Maybe the joewoodworker approach is overkill though I do think a lot of guys use the approach even with perfectly good pumps.

Anyways, I have a check valve now and secondhand SMC switch will arrive tomorrow. Also, located shops nearby to get SSR relay and power supply. All in all it’s just 25-30 USD and it’ll be fun:-)

Spent a bit of time judging and adding pinches (kinda calculating) of the needed amperage of relay and power supply. They can be very small. Even with a +100% buffer on the power supply I can get by with an 24V, 1.5A one and for the relay, a 220V, 15A will give me a 20 times headroom for start-up amperage of the motor pump. And the items are still nice and small.

[EDIT]
I just checked and my pump is indeed unreasonably bleeding itself. BUT that means, I don’t need the three-way solenoid even if I want to be nice to the pump. Because after five secs or so, it will have vented it’s own inner spaces and bit of tube. With the check valve installed, it means the pump will be starting from ambient pressure. I don’t know if it has some sort of inner bleed-off valve or whether it is actually leaking, haha.
So, far on the cheapo analogue vac meter, it says 27 ''hg. I know that doesn’t mean much. Except, I know I am more than fine for bagging purposes.

GeckoSub · September 24, 2019, 12:49pm

Success! It works:-)
It’s all wired up now and no major hick ups. The only thing I regret a tad is not really scrutinizing the specs sheet more carefully before ordering. It’s not a biggie at all but the ZSE30 which have an “M” in the model name can only show kPA units. Some of the other models switch readily between all sorts of units, which could probably have been nice. I’ll get used to it but just keep it in mind, if you are really used to, say, ''hg or bar.

Right now, the only other thing that I wish I could change (dunno if I can) is the way the hysteresis mode kicks in. As it is now, the pressure value I define (P1) will be the value which the switch will use as the low value for when to start the pump.
Say, I want to set my vacuum to -50kPa and kick in again at -48kPa - that means I have to set P1 at -48kPa and not 50 (with a hysteresis value of 2kPa).
Yeah, I know, it’s a tiny thing. Just that my brain works the other way around and again, I’ll get used to it, fast.

Anyways, I am not complaining:-) For 30 bucks (including SSR relay and power supply), this little setup can now take totally care of itself overnight. Pretty sweet.

The relay and power supply are quite small. I’ll find a plastic electronics box to encase them and the whole thing will just be 1/4 of the size of the already small pump.