Blowing off liquids

[jef]

Thanks for the replies. that’s cleared alot up.

Matt Watson:

So I understand your jump pipe/hose, connects a fuel compartment to the main line of pressure (negative in this case as it’s a pump), and then there’s obviously a hose connecting the other end of the line to the product silo… the silo must just then vent the displaced air to atmosphere?

With purely gravity fed jobs is there not another hose to vent air (or ullage) back into the tank, displacing the fuel? Or is it okay to vent fumes to atmopshere?

I ask because obviously most petrol stations have tanks that are underground and probably perfect for gravity feed, whereas most haulage yards would require the setup you’ve captured rather stylishly with your picture. Obviously most haulage firms use diesel so fumes not an issue but I would have thought in this H&S barmy day and age, with petrol or similar products, you’d have to vent the silo back into the tank rather than straight to atmosphere.

I presume “outlet lever” is a bit like a tertiary valve on a power belly tank, a bit of a failsafe further down the line and that a foot valve is the valve on each product compartment? like a pinch valve or butterfly valve on each pot or am I mistaken?

Interesting to hear that each of the discharge points on a fuel tank is dedicated to a compartment, I thought it might have been that each one was for a different fuel types as I’d imagine it’d be hard to properly clean discharge valves, as from what I gather tanks get ‘de-gassed’… again, purely personal speculation… really glad to have had so many replies.

Regarding the responses about wether or not liquid can be blown off, my thinking was that if a flow of liquid drops into a powerful flow of air (much like fuel in a carburetor) it would split up and act pretty much the same as powder anyway… a can of deodorant for example, is a liquid in a can under pressure, and comes out in a similar form to powder, again I might be mistaken but that’s why I thought I’d ask the experts

[matt_watson]

Hi jef, If you look at the rear of the tank you will see the discharge hose connected to the customers tank,this just vents into the atmosphere . When delivering petrol we have a vapour recovery hose that takes the vapour from the tanks back into the tanker then it goes back to the terminal and gets put back into vapour recovery system while you are loading.

[stevieboy308]

jef:
Thanks for the replies. that’s cleared alot up.

Matt Watson:

So I understand your jump pipe/hose, connects a fuel compartment to the main line of pressure (negative in this case as it’s a pump), and then there’s obviously a hose connecting the other end of the line to the product silo… the silo must just then vent the displaced air to atmosphere?

With purely gravity fed jobs is there not another hose to vent air (or ullage) back into the tank, displacing the fuel? Or is it okay to vent fumes to atmopshere?

I ask because obviously most petrol stations have tanks that are underground and probably perfect for gravity feed, whereas most haulage yards would require the setup you’ve captured rather stylishly with your picture. Obviously most haulage firms use diesel so fumes not an issue but I would have thought in this H&S barmy day and age, with petrol or similar products, you’d have to vent the silo back into the tank rather than straight to atmosphere.

I presume “outlet lever” is a bit like a tertiary valve on a power belly tank, a bit of a failsafe further down the line and that a foot valve is the valve on each product compartment? like a pinch valve or butterfly valve on each pot or am I mistaken?

Interesting to hear that each of the discharge points on a fuel tank is dedicated to a compartment, I thought it might have been that each one was for a different fuel types as I’d imagine it’d be hard to properly clean discharge valves, as from what I gather tanks get ‘de-gassed’… again, purely personal speculation… really glad to have had so many replies.

Regarding the responses about wether or not liquid can be blown off, my thinking was that if a flow of liquid drops into a powerful flow of air (much like fuel in a carburetor) it would split up and act pretty much the same as powder anyway… a can of deodorant for example, is a liquid in a can under pressure, and comes out in a similar form to powder, again I might be mistaken but that’s why I thought I’d ask the experts

It’s not blown off in the same way powder is, the tank is pressurised to force it off, so the air is blown into to top of the tank pressuring the air on top of the liquid. So only liquid comes out of the discharge pipe, until it’s empty anyway!

[rjan]

jef:
Thanks for the replies. that’s cleared alot up. …

Jef-I think you’re trying to draw too much of an analogy between powder and liquid tanks. It’s like trying to explain the workings of the water mains in terms of how a sandblasting machine works.

Powder tanks move particulate solids by creating a suspension of those particles in a stream of air. When it reaches the destination tank, it is allowed to fall out of its suspension in the air (which it does easily), and settles to the bottom of the tank.

Liquid tanks move liquids simply by pressurising or pumping the liquid. The principles of moving the liquid shares more in common with the air stream itself in the powder tank context, than with the powder that the air stream carries. So getting a liquid going in a liquid tank (when blowing off) is very much like getting the air stream going on a powder tank - i.e. you pressurise the tank then simply open the valves to allow it to flow.

You could fill a powder tank with a liquid and treat it like a powder, but you’d get one (or both) of two effects.

You’d either get evaporation (as you say like a carburettor), but unlike particulate solids which fall out of suspension easily, the vapour would need extensive treatment to condense it back into a liquid. This is never desirable, and in the case of flammables downright dangerous (flammable solids like flour and sugar also have this danger when suspended in air, which is why silos sometimes explode, but it’s a managed risk and a considerably lower risk than flammable liquid vapours).

Or, with liquids that don’t evaporate, you’d pour the liquid into the air stream, and as soon as it touched the wall of the pipe it would stick and crawl along the wall (like water on a windscreen when the wind is blowing). The tanker would simply empty slower (perhaps much slower) than if you let the pipe fill completely with liquid (i.e. with liquids you can use a technique which in a pipe containing powder would cause the powder to fall out of suspension and block the pipe).

Liquids are in a sense generally much easier and more consistent to move than powders - with powders there’s more of a judgment to keep the product suspended in air (without either blocking the pipe or slowing the flow to a crawl), with most liquids you just open valves and can walk away. Liquids are more difficult in the sense that they tend to be vastly more dangerous substances than you’ll find on powders, and spillages can be fatal, and so can cocktails of different products - there is therefore much more of a challenge to ensure that things are set up right to begin with, and to recover safely if things go wrong. Spillages and cocktails can also escape into a much wider area, and may cost far more to clean up and treat.

[rog270]

You shouldn’t be asking this question on this or any other forum,you should be trained by you employer to deliver the product safely,

[gingo]

jef:
Can anyone give me a brief idea of how to blow liquid tanks off?

I’ve done plenty with powder tanks and I can imagine a liquid tanks a bit like a 1 pot belly tank without pad air. Is this the case?

Also when I’ve topped powder in the dark with a looking glass on the discharge pipe I’ve noticed spark like static. How do you blow flammable off or is it just gravity fed?

youve asked about BLOWING OFF, you have been given some conflicting advice, you can and do blow off liquids,
here is my advice, first of all you connect your delivery hose to the customers tank, you connect compressor hose from the unit to pressure inlet pipe, on tank usually a 2 inch fitting. there is usually a pressure gauge attached to the inlet pipe, though it maybe on the tank, check all vents from the tank are CLOSED, cos you are pressurising the tank , NOT VENTING ,build pressure gauge up to 2 bar, then open customers valve, then open your outlet valve(s). the 2 bar pressure will push the load off, when tank is empty hose will usually shake,and 2 bar will drop cos theres no product to pressurise. close your out let valves and customers inlet valve, turn off compressor , disconnect delivery hose, and compressor hose, IMPORTANT, OPEN VENT VALVE,USUALLY ON TOP OF TANK, to release pressure in tank, hope this helps.

[gingo]

Liquids are straightforward, you pressurise the tank and then let 'er rip

basicly this,

just mind to depresurise the tank once tipt.

[lennoxtown]

Pat Hasler:
DON’T forget to vent the tank before you start to unload !!! It will implode.

Lol… that reminds me of my Dad telling me when he commited that very mistake when he was a young lad driving for an old Glasgow haulage firm James Hemphill & Sons Oops!!

Does anyone remember that company, or have any old photos?

[pat_hasler]

Well, you guys have put a new one on me LOL, Never ever heard of using air and blowing a liquid load off ? I have never in ten years with tankers even seem a liquid tank with an aid hook up ? … So glad I have my Hydropack

[gingo]

Lennoxtown:

Pat Hasler:
DON’T forget to vent the tank before you start to unload !!! It will implode.

Lol… that reminds me of my Dad telling me when he commited that very mistake when he was a young lad driving for an old Glasgow haulage firm James Hemphill & Sons Oops!!

Does anyone remember that company, or have any old photos?

you only VENT when using a pump, not BLOWING OFF, B/OFF you are pushing the load out, so PRESSURISING TANK . pumping you are sucking load out, so need to vent tank,

an exception being petrol tankers, eh matt watson ?,they are fitted with emco lids,which are vented.

remember hemphills, i worked for them after they were taken over, P+O, and hoggs of kilsyth. nae pics though.

[acd1202]

Coming back to your first comment on powders, you will only see sparks in the dark if it’s not correctly earthed. Obviously the sparks will be there in the daytime too, you just can’t see them.

It amazes me how few powder drivers understand the risks of explosion, extremely rare admittedly, but a bit like crashing aircraft, it will only happen to you the once. High risk products like PTA and some grades of Nylon will always be blown with customer supplied Nitrogen but any powder or fine granulate will spark and can explode under pressure in air.

[wirksworth_rod]

jef:
Can anyone give me a brief idea of how to blow liquid tanks off?

I’ve done plenty with powder tanks and I can imagine a liquid tanks a bit like a 1 pot belly tank without pad air. Is this the case?

Also when I’ve topped powder in the dark with a looking glass on the discharge pipe I’ve noticed spark like static. How do you blow flammable off or is it just gravity fed?

so thay did not tell you abought spark arest then on you adr or did you get it of a cornflake box little trick we play on newby tanker men when blowing sand with a roll up pipe place you leg on the pipe mate to sea if its flowing then stand back as they get a statickick of it ow goodold days

[jef]

Rjan:

jef:
Thanks for the replies. that’s cleared alot up. …

Jef-I think you’re trying to draw too much of an analogy between powder and liquid tanks. It’s like trying to explain the workings of the water mains in terms of how a sandblasting machine works.

Powder tanks move particulate solids by creating a suspension of those particles in a stream of air. When it reaches the destination tank, it is allowed to fall out of its suspension in the air (which it does easily), and settles to the bottom of the tank.

Liquid tanks move liquids simply by pressurising or pumping the liquid. The principles of moving the liquid shares more in common with the air stream itself in the powder tank context, than with the powder that the air stream carries. So getting a liquid going in a liquid tank (when blowing off) is very much like getting the air stream going on a powder tank - i.e. you pressurise the tank then simply open the valves to allow it to flow.

You could fill a powder tank with a liquid and treat it like a powder, but you’d get one (or both) of two effects.

You’d either get evaporation (as you say like a carburettor), but unlike particulate solids which fall out of suspension easily, the vapour would need extensive treatment to condense it back into a liquid. This is never desirable, and in the case of flammables downright dangerous (flammable solids like flour and sugar also have this danger when suspended in air, which is why silos sometimes explode, but it’s a managed risk and a considerably lower risk than flammable liquid vapours).

Or, with liquids that don’t evaporate, you’d pour the liquid into the air stream, and as soon as it touched the wall of the pipe it would stick and crawl along the wall (like water on a windscreen when the wind is blowing). The tanker would simply empty slower (perhaps much slower) than if you let the pipe fill completely with liquid (i.e. with liquids you can use a technique which in a pipe containing powder would cause the powder to fall out of suspension and block the pipe).

Liquids are in a sense generally much easier and more consistent to move than powders - with powders there’s more of a judgment to keep the product suspended in air (without either blocking the pipe or slowing the flow to a crawl), with most liquids you just open valves and can walk away. Liquids are more difficult in the sense that they tend to be vastly more dangerous substances than you’ll find on powders, and spillages can be fatal, and so can cocktails of different products - there is therefore much more of a challenge to ensure that things are set up right to begin with, and to recover safely if things go wrong. Spillages and cocktails can also escape into a much wider area, and may cost far more to clean up and treat.

Hi Rjan,

Thanks for the reply and for being thorough, it’s really much appreciated as I do find it interesting to know the technical details… I’m a bit of a day dreamer and I like to try and undesrtand out how stuff works.

I’ve never actually seen a liquid silo so I sort of assumed you’d be discharging up a 500 foot long pipe that went mostly upwards, and I’ve seen many a liquid tank with a blower on the side of it.

again, much appreciated.

[jef]

acd1202:
Coming back to your first comment on powders, you will only see sparks in the dark if it’s not correctly earthed. Obviously the sparks will be there in the daytime too, you just can’t see them.

It amazes me how few powder drivers understand the risks of explosion, extremely rare admittedly, but a bit like crashing aircraft, it will only happen to you the once. High risk products like PTA and some grades of Nylon will always be blown with customer supplied Nitrogen but any powder or fine granulate will spark and can explode under pressure in air.

Flour’s probably a good 'un.

Thanks for that though I didn’t realise that. All our PVC jobs have earth points but litterally none of the grit jobs (limestone) do.

[jef]

wirksworth rod:

jef:
Can anyone give me a brief idea of how to blow liquid tanks off?

I’ve done plenty with powder tanks and I can imagine a liquid tanks a bit like a 1 pot belly tank without pad air. Is this the case?

Also when I’ve topped powder in the dark with a looking glass on the discharge pipe I’ve noticed spark like static. How do you blow flammable off or is it just gravity fed?

so thay did not tell you abought spark arest then on you adr or did you get it of a cornflake box little trick we play on newby tanker men when blowing sand with a roll up pipe place you leg on the pipe mate to sea if its flowing then stand back as they get a statickick of it ow goodold days

I don’t have my ADR, I’ve worked for firms that do mostly limestone powder, soda ash etc with belly tanks and tip tanks/mobsils/bag-in-boxes for PVC resin/talc/limestone grit etc.

I’ll remember that one, never used a roll-up pipe yet though.

[jef]

Rog270:
You shouldn’t be asking this question on this or any other forum,you should be trained by you employer to deliver the product safely,

I’m only asking out of interest, I’m not going to risk my children’s lifestyle, my mortgage and my job satisfaction by changing jobs just to satisfy my curiosity, nor could I imagine any legitimate company letting me loose without the proper training anyway.

Sorry for being interested in something

[matt_watson]

Hi gingo, I worked for P&o out of Grangemouth on the Burmah petrol contract. The depot at Polmadie was still in use then they moved everything to Grangemouth. I think I’m one of the few drivers still on the fuel that worked for P&O.Good old days. Someone was looking for photos of Hemphills. If they go to Brian Edgar fotki or boballoa fotki sites there are photos on there.

[ovlov_jay]

Almost 2 full pages and no dipper

He must be bolt up with his man crush on box set

[wirksworth_rod]

jef:

wirksworth rod:

jef:
Can anyone give me a brief idea of how to blow liquid tanks off?

I’ve done plenty with powder tanks and I can imagine a liquid tanks a bit like a 1 pot belly tank without pad air. Is this the case?

Also when I’ve topped powder in the dark with a looking glass on the discharge pipe I’ve noticed spark like static. How do you blow flammable off or is it just gravity fed?

so thay did not tell you abought spark arest then on you adr or did you get it of a cornflake box little trick we play on newby tanker men when blowing sand with a roll up pipe place you leg on the pipe mate to sea if its flowing then stand back as they get a statickick of it ow goodold days

I don’t have my ADR, I’ve worked for firms that do mostly limestone powder, soda ash etc with belly tanks and tip tanks/mobsils/bag-in-boxes for PVC resin/talc/limestone grit etc.

I’ll remember that one, never used a roll-up pipe yet though.

bin on powder tanks 34 year done liquid tanks now and then as for limeston grit do that a lot now as we do most of the feed mills up and down the place blowing for 1 or 2 hours at a time you will sea our mob lomas distribution all over the place tanker men are a step up from tipper men liquid tanker men are a step up from powder men so jef looks loke your at the top of the tree best of luck with it though what ever you choose

[wheel_nut]

Think of a road tanker as an aerosol can, open the valve and air pressure forces the liquid out, sometimes a company will supply a nitrogen blanket and a pump, the blanket replaces oxygen in the case of flammable liquids or for hygiene reasons