Hydraulic Press

[Cornelius]

Hi,

I was wondering if any of you are using a hydraulic shop press (the kind that is sold for garages and metal workshops)? I have seen a number of threads on requiring huge psi values, but they always seem to be attempting them with compressed air - using an air tank or compressor with a 1 inch cylinder you are usually limited to a range up to 200psi (divide that by the surface area of your mold and it is much less). Those shop presses also have a 1 inch cylinder, but can apply 12 ton of pressure ... They even seem a pretty good deal for much lower psi applications. The unit I am linking here is not even that expensive ($200), but they come even cheaper (at $80) if you get a 4 ton version without gauge. There obviously will be a slight pressure drop during the initial hour as the cheese actually compresses, but you can read that on the gauge and crank a little more - after the first hour I don't think the piston will actually move down enough to change the force acting on a cheese.

Now, am I might be missing something crucial, should I keep my hands off? I have had a lot of silly ideas in the past, please keep me from committing yet another mistake ...

P.S. obviously found it on ebay, here is a link:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&_rdc=1&item=360260108927

[wharris]

IMHO,
I do not think that a hydraulic press will work as well as an air cylinder.  This is actually addressed way back in some threads that i am too lazy to go find.....

The issue here is consistancy of applied pressure.  As you press a mound of curds, the curds will express whey. And as whey is expressed, the overall size of of the cheese shrinks.  This shrinkage will reduce the pressure on the wheel if the wheel is being compressed by a hydraulic press. In order to compensate for this, you would have to continually apply more pressure to keep the pressure on the wheel of cheese consistant. This is due to the compressability of hydraulic oil.  (it isn't)

The compressability of air, however, is like a spring. That is, as whey is expressed using an air-cyclinder, and the wheel shrinks, an air-cylinder will simply expand slightly to compensate for that shrinkage with virtually no loss in pressure. The pressure would remain the same.

The bottom line is that the pressure appied to a wheels of cheese is way more consistant over time with the use of an air-cyclinder as opposed to a hydraulic jack/cylinder.

Although you are right in that a hydraulic press can apply a LOT more more pressure.  The issue is just consistancy.

[Cornelius]

Hi Wayne, thanks for your quick reply!

That is certainly an issue worth debating (I actually attempted to bring it up, but in a very convoluted way). Yes, the cheese compresses, but from my experience only in the early stages of pressing (when I also flip and redress frequently giving me a chance to adjust pressure anyways) - do you think for the last 6-8 hours of a pressing session the cheese compresses enough to require constant adjusting? (I am asking because I actually have no idea).

My second thought (and again, I don't really have any idea) air systems obviously use regulators (and being a diver I am happy to report they work really well because my lungs would otherwise be shot by now) ... are there no regulators for hydraulic systems? If you cranked the hydraulic pressure and placed a regulator in line to your piston, wouldn't you be able to achieve a constant pressure on your piston? I understand that hydraulic oil isn't compressible and this is what makes it do what it does - and an air pressure regulator kind of uses the principal of different ratios of compression, but hey, maybe there are such things as hydraulic regulators (if indeed it is necessary to make constant adjustments)?

I simply don't know enough about it, that's why I am glad I asked here on the board! 

btw, aren't there a lot of those little spring cranked presses out there ... they will reduce pressure considerably as the cheese compresses. Maybe there are forum users out there who can tell me how often/frequently they readjust the crank ...?

Thanks!

[DeejayDebi]

I ask about that about a year ago too. Someone had them for like $55. Look like a good option for multiple cheeses. I think the concerns for the cheese shrinking could be easily overcome by adding a counter weight to the table or springs or some such thing.

[Cornelius]

Hello Debi & Wayne,

Sorry, I didn't mean to double post - I did actually search for hydraulic presses and other keywords, but nothing came up. Neither on comparison of air vs. hydraulic. 

In any case, I looked a little further into the idea and there do seem to be be some kind of hydraulic regulators, but I am not sure if they would do what I want them to do. One could obviously go to the extreme of adding a pressure sensor and run that to a PLC. Using a hydraulic pump one could then keep a constant pressure - as a matter of fact one could even program a gradual increase of pressure over time (most recipes ask for low psi first and end with a great multiple). I suppose that would be nice, but it adds another couple of hundred dollars and is more involved than I would want it to be.

However, I did come across a shop press that is advertised as air-hydraulic:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220596501162

Now, the unit seems almost identical to the basic hydraulic one, only that it must have an air-cylinder as well. Exactly how they interact and if this setup could solve the issue of a compressing cheese, I don't know. Specs list air pressure at 120-200psi, however, it is a 20 ton press ...  so, does that mean I can keep a hydraulic cylinder at constant pressure via an air-cylinder controlled by an air-regulator? Would be sweet, but I am probably only dreaming. Wayne, any idea if and how this might work?

Thanks for your input!

[wharris]

I ask about that about a year ago too. Someone had them for like $55. Look like a good option for multiple cheeses. I think the concerns for the cheese shrinking could be easily overcome by adding a counter weight to the table or springs or some such thing.

If you added springs, to compensate, the springs would needs to have the same compressive force as the press in order to keep consistant pressure.

I would suggest that if you bothered to to use springs in that fashion, you might as well just use springs for the whole press. Which, by the way,  is why spring-type cheese presses are popular.  The spring keeps a constant pressure.

just my 2 cents.

[Cornelius]

Hi Wayne,

I agree on the spring matter, only that you would need a hydraulic press in order to actually achieve 12 tons of pressure (if that is what you want to use on your cheese) - I don't think you can hand crank a spring press to that kind of force (and I don't mean because of material failure).

However, my idea would be to use the press without an added spring system - do you have any thoughts on that link I added above? What exactly do they mean by air/hydraulic and might this combo actually do what I am looking for?

Many thanks.

[wharris]

I will be honest, i have not read that link (yet) as I am at work.......

But my off-hand thoughts are that for a home cheese maker, a press like that is too complicated...

I would use suggest leveraging gravity to press your cheese. Its very constant... 

[Cornelius]

I totally agree      just that I get excited sometimes and dream ...

[DeejayDebi]

That is very similar to the one I was looking at but I was looking at a 5 ton press.

[Cornelius]

Hi Debi,

Yes even 5 ton would be plenty for me  - I usually make white mold ripened soft cheeses and only recently attempted a couple of Tommes (but they don't seems to need a lot of weight). I have made some alpine cheeses that require a fair amount of pressure, but using a 4" mold still keeps it in check.

I actually posted this more as a suggestion for somebody who is making cheddar or other cheeses in large molds, requiring several tons of weight. And for somebody who wants to press upward of 10psi, I think this might still work - especially for a hobby cheese maker. Who ever leaves their cheese unattended anyhow (at least I don't). I constantly monitor it and flip it for the fist couple of hours - by the time you apply full force and you go to bed, I think the cheese is mostly compacted and you don't loose that much pressure over the final 5+ hours of pressing. And these shop presses are cheep!

All that being said, I did come across a listing for a pneumatic cylinder on ebay with a 100mm bore for only $25. If you use an 8 inch mold and 200psi air pressure you end up with approx 48psi pressure on your cheese - or the equivalent of balancing 2400 lbs on your cheese! That's probably more than enough for any cheese I plan on making ... ever!

So, yes, air it is - not only because it can provide more than enough pressure needed, but also because it is more consistent (as Wayne points out).

I just hope I don't ever get my fingers caught in there somewhere 

[MarkShelton]

I just wonder what kind of mold will stand up to a 12, or even 5 ton pressing... unless you're pressing some pretty huge wheels, or an entire bench of small cheeses at once.

[wharris]

Moulds have breaking points!

I broke my 8" mould!

Bent the follower back actually....

[DeejayDebi]

I wonder if these things are adjustable? Maybe change a valve or something?