Relief Valves

[tipk99]

Any reason one of these...

http://www.grainger.com/category/vacuum-and-pressure-relief-valves/valves/pneumatics/ecatalog/N-aiv?bc=y#nav=%2Fcategory%2Fvacuum-and-pressure-relief-valves%2Fvalves%2Fpneumatics%2Fecatalog%2FN-aivZ1z0o38b%3F_%3D1386215369861

Wouldn't make a good pressure relief valve?

Tom

[Panoscape]

What is the PSI rating of your tank? These must be under that rating. The link shows that these are for 25 to 200 psi, thats pretty strong. My SS drums have a rupture level of 15-20 psi so I'm using 1 psi pressure and vacuum valve. If running a still with a thumper you're going to have more vacuum than external pressure so make sure it does both.

Some on a budget use a piece of high temp plastic film and clamp it on a ferrule. The plastic film will burst before the still will.

[tipk99]

Most of those valves are 0-20 psi, and adjustable.... only one is 25-200. My still would be very low or no pressure hopefully...

[PeteB]

A relief valve needs to more than just trigger at a set pressure.

I think the valves in that link are physically too small to be able to let off the pressure fast enough if / when things go pear shaped (unless you have a tiny still)

Since I started distilling I have twice forgotten to turn on the cooling water.

I have a 7 inch diameter relief valve that pops competly open when there is too much pressure.

When it popped there was a 7 inch gueyser of foam going about a foot into the air. If you tried putting that through a 1 inch valve it would have done almost nothing to stop the pressure building.

[HedgeBird]

PeteB, Can you elaborate on how not turning on cooling caused a pressure build up in your system? My thinking was that not having cooling on would result in steam/vapor exiting the still but not a pressure build up?

tipk99,

This is the relief valve I am using on my still. Pressure and vacuum combined, but a bit pricey:

http://www.glaciertanks.com/Pressure_Relief_Vacuum-Pressure_Relief_Valves_Vaccumm.html

I also put these valves on my mash-tun cooling jacket. These could be nice as you can put a pipe on the exit to direct potential escaping vapor to a "safe" spot like the floor.

http://www.amazon.com/gp/product/B002KTZB4Y/ref=wms_ohs_product?ie=UTF8&psc=1

http://www.amazon.com/gp/product/B002KU0WV0/ref=wms_ohs_product?ie=UTF8&psc=1

[Artisan Still Design]

it depends n the application. those look to be good for a pressurized air system, but if this is for a still I wouldn't recommend their usage.

Look for an over pressure valve that you can pipe from the output to vent outside or to somewhere away from potential ignition sources.

also make sure its ASME compliant, it should say ASME right on the valve itself, the inspectors will be looking for this.

I personally would use those second set of valve you've shown for your still. and a separate Vacuum relief, but I wouldn't depend on the vacuum relief at shut down, open a manual valve as the system is cooling, the amount of vacuum a still can generate could quickly overpower a small relief valve.

[tipk99]

PeteB, 7" sure seems excessive... CleaverBrooks 15 HP, 500kbtu, 15# low pressure steam boilers come with a 1.5" pressure relief valve. And I'm guessing they have a higher duty requirement than any stilll... The idea isn't to instantly depressurize your still, but to jus relieve pressure faster than its being added, correct?

HedgeBird, thank you for the links, I considered the glacier valve too, but was looking for more cost effective and really like the idea of piping away from the still.

Artisan, what valves do you use on your stills? Or do you have them made?

Thanks everyone!

[Artisan Still Design]

we use standard 1"NPT 15 psi overpressure valves.

yes these are used as a safety, not to regulate. if these go off, something very bad has happened or is about to.

[tipk99]

Thanks artisan... Are they stainless or brass?

[Sorghumrunner]

and what about vacuum relief? would a check valve pointed towards the inlet work for this?

[Artisan Still Design]

Brass is more common, as long as its ASME

[PeteB]

and what about vacuum relief? would a check valve pointed towards the inlet work for this?

There are several designs of check valves (=non return) that I have seen. The simplest with a flap on a hinge may not be so good on a simple pot still with no plates. When these are boiling I have watched the pressure and they regularly go into slight negative pressure. With a swinging flap they would quite possibly 'sniff " air which would then expand and go positive pressure and start surging. I don't know if plated stills have pressure surges.

With the valve in a vertical position and the flap on top I guess it would work well.

Other check valves I have dissected have a light spring holding a tapered plug onto a seat. In my opinion these would work well.

Thanks for the idea, I am going to put one of these on my still in the next few days.

PeteB, Can you elaborate on how not turning on cooling caused a pressure build up in your system? My thinking was that not having cooling on would result in steam/vapor exiting the still but not a pressure build up?

Look at the smallest pipe in the spirit path of your still. It is probably where the spirit trickles into your collecting tank. 1/2 inch ? You possibly have a parrot on it.

If you have even a smallish commercial still it could be producing 50 Kw of steam, that is a lot of volume (I will edit in this volume when I find the calculations)to push through a 1/2 inch pipe and you will get a lot of back pressure.

But a much more serious problem arises if you are boiling a wash that foams badly. The much higher viscosity foam could be trying to escape through that 1/2 inch pipe. With 50 Kw behind it will need to escape through a much larger orifice, if there isn't one it will probably create its own.

If too much pressure builds at the foaming stage, and then the still ruptures, the pressure suddenly drops and much of the contents will instantly boil and foam. Very serious problem for anyone near the still

The above examples are not just theory, they have happened to me and/or my friends

PeteB, 7" sure seems excessive...

Yes it is excessive but that 7 inch hole is also my manway. (There is also a much larger one but it is not as convenient to open.)

It is a piece of 7 inch pipe, with a slightly larger blanked off cap fitted over it. There is a soft neoprene o-ring that rolls in-between the 2 pipes as the cap is pushed on. At 1 or 2 psi the cap will be pushed off as it rolls the o-ring.

[PeteB]

we use standard 1"NPT 15 psi overpressure valves.

yes these are used as a safety, not to regulate. if these go off, something very bad has happened or is about to.

Steve, please don't take this the wrong way, I am learning here all the time.

Why put a 15 psi OP valve on a still that I assume runs normally at under 1 psi.

For that valve to open, your still would be operating in a range that would possibly need it to be certified as a pressure vessel! Maybe it is.

I would rather a safety device operated well before "something very bad has happened or is about to."

[HedgeBird]

Look at the smallest pipe in the spirit path of your still. It is probably where the spirit trickles into your collecting tank. 1/2 inch ? You possibly have a parrot on it.

If you have even a smallish commercial still it could be producing 50 Kw of steam, that is a lot of volume (I will edit in this volume when I find the calculations)to push through a 1/2 inch pipe and you will get a lot of back pressure.

Foaming I can understand as a potential source of pressure build up, but I still find it hard to image that no cooling and vapor/steam going out a 1/2 inch collection pipe or parrot would create pressure. My 350,000 BTU steam boiler will not build pressure when I open the 3/8" steam strainer drain (the smallest valve on the system).

My pressure relief valve on my still is currently located at the top of my column. If I get foaming in that tank that was able to stop-up the column then my valve would be just about useless. I am buying another valve today to add to the dome of the still. Also going to add vacuum valves to the still, mash tun steam heat plate and still kettle jacket. When I piped in my steam units vacuum was not something I was well aware of. I am now very much aware of it..

Here is the vacuum valve I am looking at using:

http://www.amazon.com/Watts-Water-Technologies-N36-M1-Service/dp/B002ZQ0OY4/ref=pd_cp_hi_0

[Artisan Still Design]

Steve, please don't take this the wrong way, I am learning here all the time.

Why put a 15 psi OP valve on a still that I assume runs normally at under 1 psi.

For that valve to open, your still would be operating in a range that would possibly need it to be certified as a pressure vessel! Maybe it is.

I would rather a safety device operated well before "something very bad has happened or is about to."

because that is what is required by code.

like you said, your still should never hit 1psi let alone 15.

you ought to have other mechanisms and procedures to make your still "Safe".

My view is, if something has gone so wrong that this valve is tripped, make sure you send the output to a safer place than where you are working.

but this valve realistically should never trip, but it is still required.

[meerkat]

I am afraid that I might come across as a prophet of doom here, but I am concerned that some members may not fully grasp the dangers - both physical and legal - involved. If you feel that I am being alarmist then I apologise, but I would like to highlight a few factors.

There are laws that govern the operation of vessels under pressure. They vary from country to country, but generally any vessel that contains a gas or a boiling liquid at a pressure above 5 psig would fall under the regulations. This means that you must not allow your still to operate above 5 psig and you probably want to limit it to about 1.5 psig to be safe. If you have a pressure relief valve that is set to above 5 psig it means that you are expecting your vessel to get to that pressure and if it is not registered as a pressure vessel the chances are that you are breaking the law.

PeteB gave the example of a 50 kW boiler generating steam that is being forced through a 1/2 inch pipe. 50 kW is close to 170,000 btu/hour and using the rule-of-thumb that 1,000 btu makes 1 lb of steam we have about 170 lb/hour of steam. Forcing this through a 3 ft length of 1/2" pipe would give a pressure drop of about 4 psi. It is not surprising he popped his valve which opens at 1 or 2 psig.

HedgeBird also gave an example where a boiler was unable to come to pressure if a 3/8" valve was left open. It depends on the actual valve involved but I estimate that it would require 45 psig to drive 350 lb/hr through that valve.

The lesson to learn from these examples is that putting a 1/2" relief valve on your pot is not going to give adequate protection unless you have a very small steam/heat flow. Valves that will operate reliably at these low pressures are expensive. I have successfully used water seals to protect low pressure tanks. The advantages are that they can be made fairly cheaply in the workshop and they will relieve at very precise pressures. The disadvantages are that you run the risk of drawing the water back into your pot so it must be kept clean, and once it blows it will not re-seal itself the way a spring operated valve will.

Protecting a tank against vacuum is also important. We have all seen or heard of instances where a tank full of steam or vapor has cold water sprayed into it and the whole thing implodes in milliseconds. It is very hard to protect against that. The manway should always be opened before cold water is introduced. But you also need to protect against vacuum that can be developed slowly as the still cools down. This can be done with a vacuum relief valve as described by HedgeBird or, as mentioned by others, with non-return valves. I have used disc type check valves with the spring removed and mounted on an elbow facing downwards. The weight of the disc and the pressure in the still will keep it sealed under normal operating conditions, and when a vacuum arises the weight of the disc is quite easily overcome. A water seal can also be made to serve the double duty of pressure and vacuum relief.

And whatever relieving device you use, it must of course discharge to a safe location. If you are in any doubt over the safety or legality of your installation it is worth calling out a registered pressure vessel inspector and getting the benefit of his knowledge of the local regulations.

[Artisan Still Design]

I've seen several distilleries run a pipe off the top of their still into a 5 gallon bucket of water.

this works as a overpressure relief and as a vacuum break.

only problem is this gives you in the area of 1/2 psi, you would need over 10ft of water to approach 5 psi.

if it does overpressure and blow, most of the ethanol will be trapped in the water, so its fairly safe.

if you do get a vacuum, it will suck the bucket dry, then draw in air, again pretty safe.

I like the idea, but not sure how to "package" it so the inspectors will be happy, all they see is a place for ethanol to escape.

Steve