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Re: Liquid Overfeed Systems
having built recirculator packages for many years i have found that the majority of the problems have been not following the pump company guidelines.
Pumping volatiole liquid like ammonia or ***** is easy if you have enough npsh and keep the pd down with proper inlet sizing i think Iceman was all correct in his observations
I mostly saw npsh problems causing the most difficulties.
I also like the seperate suction lines in lieu of the common drop leg.
Sometimes i have found engineers overthinking the problems.
i never tried it but i want to put in some of the witt pumps simply hanging from the vessel. with the suction straight into the pump inlet. with a valve of course.
Have seen a few sketches of this but never seen it in practice.
Would really save us on installing cost. Anyone do it ?? and what problems or success have you had.
David in texas
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Re: Liquid Overfeed Systems
Hi David,
Quote:
I mostly saw npsh problems causing the most difficulties.
I agree. These are normally the result of too much inlet loss, insufficient static head, or the pump is not setup properly allowing it to run out on the pump curve.
Quote:
i never tried it but i want to put in some of the Witt pumps simply hanging from the vessel. with the suction straight into the pump inlet. with a valve of course.
I have a friend who told me was thinking of this for some Cornell pumps. He was planning on using high-performance butterfly valves for the suction valve instead of an angle valve.
If the suction valve was a globe style in the vertical suction line, I think you would loose more than you can gain because of the inherent extra length of the globe valve.
Using a high-performance butterfly valve would of course drastically reduce the equivalent pressure loss.
I should check in with him and see what the results were. Thanks for reminding me of that.
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Re: Liquid Overfeed Systems
I installed Witt pumps type HRP 3232. They hang directly under the separator (with only a ball valve in between if you want). Works superb, easy to install, insulate and to service. As we always use one stand-by pump, the piping as shown in the attached file is standard. It clearly shows the advantages of the pump directly fit to the separator. However, only one capacity available at Witt(for now that is). Find info in the WITT HRP manual at th-witt.com.
As for the pipe inserted into the dome; as to my understanding that was invented to prevent falling oil from the separator to enter the pump, but being collected at the bottom of the dome.
We always use leg's as drawn in the attached file. Very little (never) problems with oil in the pumps.
Also standard is the use of a pressure regulator near the pump. That, with a good(!) discharge head of the pump makes it easy to set the regulating valves, and the system will be very stable. No need to go to the end of the wet return line.
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1 Attachment(s)
Re: Liquid Overfeed Systems
****, forgot the drawing.
This will be better I think.
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Re: Liquid Overfeed Systems
Very nice drawings Nico. Thank you for sharing these.
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by Nico
****, forgot the drawing.
This will be better I think.
If I'm correct, the pumps are shown on the left side of the drawing, and you have the suction pipe taken out on the bottom of the drop leg... am I correct?
On ***** R-22 this will work fine, as the oil will gather in a "layer" around the top of the liquid head...
but on ammonia, you will have no way of draining the oil before it enters the pump and is flushed out into the system along with the liquid ammonia.
As I have shown previously in this thread.. (I know might sound like a "know it all" in showing this again... but I know it works)
http://upload.pbase.com/image/62209774.jpg
(added some english text in the picture)
Notice that there is a ring around the drop leg preventing oil from draining down into the dropleg, there is a seperate dropleg for draining of oil... and as a precaution, there is an oil drain valve on the dropleg just in case :)
Just have to say that I'm not a big fan of having any important pipes going out of the bottom of a dropleg like that, cause any "contamination" in the plant that finds it's way to the liquid tank will go straight into the pumps.
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Re: Liquid Overfeed Systems
Generally in the large overfeed system has liquid feed pumps which supply liquid refrigerant to the evaporators.
I think your system must have multiple evaporators. I have read that your system has separate lines connected to pumps. This is not advisable.There must be a common header between vessel & pumps.I have handled very large overfeed ammonia system.If any querry pls write to me.
Thanks
AMARNATH JHA
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by AMARNATH JHA
I have read that your system has separate lines connected to pumps. This is not advisable.There must be a common header between vessel & pumps.
Can you explain your comments please?
Thanks.
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Re: Liquid Overfeed Systems
Both left and right side of the drawing are of a separator with pumps. One with horizontal and one with vertical shaft. The top is a detail of the oil dome with ammonia down pipe to the pump(s) in the middle. The system is for Ammonia indeed! As oil is more heavy than Ammonia, it will fall down to the bottom of the separator, and than sort of fall off the edge into the oil dome. Ammonia is collected just 10mm higher than the bottom of the separator. That's why the vortex breaker is so important.
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1 Attachment(s)
Re: Liquid Overfeed Systems
This detail will be more clear I guess.
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Re: Liquid Overfeed Systems
Hi Nico,
Thanks for posting the drawing on the sump details.
Do you work for a contractor, manufacturer, ???
What type of liquid feed control valve are you using to maintain a constant liquid level in the vessel?
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by Nico
This detail will be more clear I guess.
Ah, thanks Nico, that was the part I was unsure about :)
In the previous drawings it seemed like you fed the pumps from the bottom of the dropleg :)
as you see in my drawing, we take it out on the side, and the bottom of the vortexbreaker has a triangular opening cut into it, allowing oil to drain to the bottom of the dropleg if it happens to enter into the vortexbreaker...
The votexbreaker you use, is it just a "cross" of flatsteel welded across the top of the suction line?
cant say other that different solutions same result :)
tho I cant say other than your solution looks as good as any, I'm stuck in my ways and I'm gonna do it [Sings]Myyyyy waaaaaaaaaaaay[/sings] :d
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by US Iceman
Hi Nico,
Thanks for posting the drawing on the sump details.
Do you work for a contractor, manufacturer, ???
What type of liquid feed control valve are you using to maintain a constant liquid level in the vessel?
wouldnt a system be in a somewhat equilibrium, depending on how many "consumers" are in use, in regards to the liquid level in the LP vessel? less consumers = higher level and all.
When I calculate the ***** charge I go by rule of thumb :) 1 vertical freezer = 5 x 57 Kg (5 x 125 pounds) or 5 bottles of *****.
a normal cargohold on a ship is approx 2-5 bottles
Usually we charge from 800 Kg (17681 pound) tanks on a new system, and as it goes, I'll just open the consumers one by one till I loose pump pressure.
when I loose pump pressure I'll wait to open the next consumer till I have pump pressure again, then rinse and repeat till you have pump pressure with all consumers running.
Of course you gotta keep an eye out so you dont charge more than the capacity of the LP reciever/tank... I never charge more that 80% of the LP reciever volume, it's the law, and no way no how anm I going to be struck down by some insurance company for either destroying a ship, or wrecking a compressor :)
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Re: Liquid Overfeed Systems
Hi Tycho,
Quote:
wouldn't a system be in a somewhat equilibrium, depending on how many "consumers" are in use, in regards to the liquid level in the LP vessel? less consumers = higher level and all.
Yep, if the system is something similar to a critically charged system, which may be what you are describing.
On some systems there might be a need to control how much liquid enters the vessel, which is how I see most of the liquid overfeed systems (except those designed for a critical charge).
I have seen some level controls using a simple float switch controlling a solenoid. Others might use a capacitance probe and a modulating liquid feed valve.
I was wanting to see what type Nico used.
Quote:
I never charge more that 80% of the LP receiver volume...
Is this when the system is being commissioned? Hopefully, not 80% full when operating at full load.:eek:
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Re: Liquid Overfeed Systems
As a one man company I work for several big contractors and manufacturers,as well asfor larger users. I (try to) help with design / commisioning / training and trouble shooting. Always traveling. Lots of fun!
The level control of the separator depends on the country (regulations), the system and the budget.
When there are lots of small clients, than you can work with a simple level switch, solenoid valve and regulator valve from a liquid receiver.
If you have an analog level sensor, you can use the same valves and program a proportional pulse pause regulator or -if you have the monney- a regulator valve. I know that the Danfoss SV float regulator with PMFL valve works perfect for decades.
A high pressure float valve gives you the lowest NH3 charge (I like that), but most clients want to see a good level in a large Ammonia vessel (Middle East and Africa). Your separator will be exspensive (large) with a HP float valve, but you don't need a liquid receiver.
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Re: Liquid Overfeed Systems
Quote:
Your separator will be expensive (large) with a HP float valve, but you don't need a liquid receiver.
I have done this on several projects and really like it. If the float valve is sized properly you can allow the compressor discharge pressure to decrease to really low pressures (if everything else is sized correctly).
Works great!
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by US Iceman
Hi Tycho,
Is this when the system is being commissioned? Hopefully, not 80% full when operating at full load.:eek:
Yes, on commisioning, and 80% with all the consumers defrosted :)
Quote:
Originally Posted by nico
-I know that the Danfoss SV float regulator with PMFL valve works perfect for decades.
on all our plants older than 5 years we used the danfoss SV-1 HP float with a pilotreciever with about 40 liter capacity, worked like a charm
we still use the sam pilotreciever, but are now using danfoss AKS level transmitters... lots of trouble with them in the beginning, with them failing after a short time and so such... but with feedback from all the users danfoss has weeded out most of the problems and we now use this solution up against either AKV valves or PM valves.
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Re: Liquid Overfeed Systems
Have not seen the AKS 41(?) yet.
Do you use the EKC 347 as an controller, or direct to the PLC?
What do you use as control valve?
I have used the RTK NI1321 a lot. Problem with this sensor is that they are density sensitive. If the evaporating temperature changes, than you get an offset.
We always controll through the PLC. With one click you program a controller, so why install others?
For regulator valves we are often directed by the client's standard; Samson, Worchester etc. We use RTK Kornwestheimer as our "standard".
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Re: Liquid Overfeed Systems
Hi Tycho,
Quote:
Yes, on commissioning, and 80% with all the consumers defrosted
OK, I'm assuming that when the vessel is 80% full the load is is very small. If the vessel is 80% full, I would think this would limit how much compressor capacity you could have ON during this time.
The separation space in the vessel would be very small. I'm also assuming you have really good controls to limit how fast the users can be activated and how fast the compressor(s) load up to prevent liquid slugging.
I suppose the reason I raised the question in the first place is... Someone who is not familiar with the particular requirements you normally see may assume this is standard practice for any overfeed system.
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1 Attachment(s)
Re: Liquid Overfeed Systems
Hi,
on attached drawing you can see the old fashioned way of level control, pump protection and compressor protection if customer does not like to spend to much money ;)
Attachment 1033
All is working Ok.
Yes, one pump is stand-by.
Best regards,
Josip :)
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Re: Liquid Overfeed Systems
Hi Josip,
Are those strainers/filters in the suction line to the pumps?:confused:
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Re: Liquid Overfeed Systems
Hi, US Iceman
Quote:
Originally Posted by US Iceman
Hi Josip,
Are those strainers/filters in the suction line to the pumps?:confused:
Yes, and mostly on new plants during start up, we have to clean them often. Also they are bigger then the pump inlet connection. Pumps are Hermetic CAM 2/3 with Qmax and Qmin orifice.
That filter we install as the lowest part of the pump inlet pipe.
See you are :confused: , but we have to protect pumps (on ammonia plants with dirty black steel separators and pipes) on some way, but that is another long story ;) .
Best regards,
Josip :)
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Re: Liquid Overfeed Systems
Hi Josip,
What you say makes a lot of sense. The carbon steel pipe can be dirty with the scale that comes in the pipe.
Do you normally find a lot of weld slag in these strainers?
Do you use weld rings (not sure what you might call them)? They fit inside the end of the pipe to help with alignment and help to prevent weld slag from blowing into the pipe.
Have you tried pickled pipe before? This is very clean, but must be protected until the insulation and paint are applied to the pipe.
Here in the US we normally allow the strainers before the solenoid valves to catch this junk.
The strainers in the pump suction line add pressure drop which decreases the net positive suction head on the pumps. This can cause cavitation.
You are correct. This could be a long story.;)
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by US Iceman
Hi Josip,
What you say makes a lot of sense. The carbon steel pipe can be dirty with the scale that comes in the pipe.
Do you normally find a lot of weld slag in these strainers?
Do you use weld rings (not sure what you might call them)? They fit inside the end of the pipe to help with alignment and help to prevent weld slag from blowing into the pipe.
Have you tried pickled pipe before? This is very clean, but must be protected until the insulation and paint are applied to the pipe.
Here in the US we normally allow the strainers before the solenoid valves to catch this junk.
The strainers in the pump suction line add pressure drop which decreases the net positive suction head on the pumps. This can cause cavitation.
You are correct. This could be a long story.;)
I have always seen a strainer in the pump suction line, pumps can be quite expensive and systems can be dirty:eek:
Probably a good idea to remove the strainer after a year or so use or fit a large mesh nut and bolt catcher at this point.
Small mesh strainers can become oil traps on LT systems, best to avoid smaller mesh strainers on these types of applications.
Backing rings were fitted in the past, but now we are more advanced:D
TIG welded roots are the norm with the filler and cap in stick:)
Kind Regards Andy:)
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Re: Liquid Overfeed Systems
Hi Andy,
Quote:
I have always seen a strainer in the pump suction line, pumps can be quite expensive and systems can be dirty:eek:
Probably a good idea to remove the strainer after a year or so use or fit a large mesh nut and bolt catcher at this point.
Small mesh strainers can become oil traps on LT systems, best to avoid smaller mesh strainers on these types of applications.
Absolutely no doubt the systems can be quite dirty.
What size mesh screens do you use for low temp and higher temp. applications?
I'm not disagreeing with the use of strainer, just saying the pressure drop should be accounted for in the pump NPSH calculations. The pressure drop of this device could add a meter or more of head required for the pump suction. (just a guess, but it's probably something like this)
Quote:
Backing rings were fitted in the past, but now we are more advanced:D
TIG welded roots are the norm with the filler and cap in stick:)
Are you saying I'm old fashioned?:p
I would prefer exactly what you are doing Andy. This makes a much better weld. I always suspected the backing rings could collect junk under the collar and create a potential corrosion site from inside. I also think the weld rings are harder to read in an x-ray.
Do you use consumable inserts for the first pass TIG weld? Or, just simply fit them up by hand? Or, use a pipe alignment fixture.
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by US Iceman
Hi Andy,
Absolutely no doubt the systems can be quite dirty.
What size mesh screens do you use for low temp and higher temp. applications?
I'm not disagreeing with the use of strainer, just saying the pressure drop should be accounted for in the pump NPSH calculations. The pressure drop of this device could add a meter or more of head required for the pump suction. (just a guess, but it's probably something like this)
Are you saying I'm old fashioned?:p
I would prefer exactly what you are doing Andy. This makes a much better weld. I always suspected the backing rings could collect junk under the collar and create a potential corrosion site from inside. I also think the weld rings are harder to read in an x-ray.
Do you use consumable inserts for the first pass TIG weld? Or, just simply fit them up by hand? Or, use a pipe alignment fixture.
We use filters in the range 40 to 100 micons range, quite fine really:D I favour big bore long drop legs, put the surge drum on one floor and the pumps on the floor below with a straight line down into the pump (vortex breaker at the top of the pipe, ball valve at the pump, all say 6" on a 2 1/2" or 3" inlet pump.
TIG root is not used with a ring. The pipe is champhered, with the slope creating a vee for the weld to be built up in. The pipe or fitting is gapped by 2 to 3mm all the way round, to allow a weld bead to form evenly on the inside of the weld, much like a mini cap on the inside.
Kind Regards Andy:)
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Re: Liquid Overfeed Systems
Hi, US Iceman :)
Not to much of weld slag (nowdays mostly use TIG for root weld) but lot of particles remain after grinding to make a cone for weld. this you have even with sand or CO2 blasted pipes.
I have to admit about weld rings and backing rings I do not know, because, never used them (please, post a link or some picture ;) ). We used sometimes alignment tool for pipes (in case of X-ray) but mostly doing that by hands of experienced pipe fitters ;) , faster and cheaper.
Yes, installing filter in front of the pump will reduce NPSP but filters are of very big size and pressure loss is very small.
I think Andy, did explain almost all but in much better english than me :D , thanks Andy;)
Quote:
Originally Posted by Andy
We use filters in the range 40 to 100 micons range, quite fine really I favour big bore long drop legs, put the surge drum on one floor and the pumps on the floor below with a straight line down into the pump (vortex breaker at the top of the pipe, ball valve at the pump, all say 6" on a 2 1/2" or 3" inlet pump.
TIG root is not used with a ring. The pipe is champhered, with the slope creating a vee for the weld to be built up in. The pipe or fitting is gapped by 2 to 3mm all the way round, to allow a weld bead to form evenly on the inside of the weld, much like a mini cap on the inside.
best regards,
Josip :)
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Re: Liquid Overfeed Systems
Andy,
Quote:
Originally Posted by Andy
TIG root is not used with a ring
Depnding on the customers pipe welding specification it may be called for. Here are some links to suppliers of these. We used these when the specifications were very stringent in chemical plants.
They are ordered in the same material as the pipe, with the inserts being consumed during the fusing process. They make a really nice joint, which sometimes is hard to tell the joint from the main pipe.
http://www.robvon.com/html/proc_consum.html
http://www.robvon.com/html/consumables.html
Main page:
http://www.robvon.com/
Also see their link for backing rings. This is listed on the left hand side of the webpage.
http://www.imperialweldring.com/new/consumable.html
Josip,
Quote:
...you have even with sand or CO2 blasted pipes.
I have used sand blasted pipe before but never CO2. Does this work well? I'm assuming they use dry ice for the blasting right?
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Re: Liquid Overfeed Systems
Hi, US Iceman
thanks for links, very good things (kind of VFD for pipe fitters and welders ;)
http://www.cryogenesis.co.uk/
Yes they use dry ice and complete work is very clean. I did not use it but got some info about from my friends.
Best regards,
Josip :)
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by Nico
Have not seen the AKS 41(?) yet.
Do you use the EKC 347 as an controller, or direct to the PLC?
What do you use as control valve?
I have used the RTK NI1321 a lot. Problem with this sensor is that they are density sensitive. If the evaporating temperature changes, than you get an offset.
We always controll through the PLC. With one click you program a controller, so why install others?
For regulator valves we are often directed by the client's standard; Samson, Worchester etc. We use RTK Kornwestheimer as our "standard".
We make our own control system with PLC and the AKS is wired directly to the PLC, with readouts and calibration made possible from the plc display.
we have also retrofitted older systems with an AKS working with a EKC 347... Works fine with either...
Had some problems with the EKC tho, not sure what was done, but the electrician doing the wiring also powered up the system before I got there, and managed to burn out the contacts on the EKC, so I had to use the alarm contact for either hi or lo level, cant remember... the customer is non the wiser and the system works :)
We use mainly Danfoss valves, ranging from ERV to PM (depending on system size)
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by US Iceman
Hi Tycho,
OK, I'm assuming that when the vessel is 80% full the load is is very small. If the vessel is 80% full, I would think this would limit how much compressor capacity you could have ON during this time.
The separation space in the vessel would be very small. I'm also assuming you have really good controls to limit how fast the users can be activated and how fast the compressor(s) load up to prevent liquid slugging.
I suppose the reason I raised the question in the first place is... Someone who is not familiar with the particular requirements you normally see may assume this is standard practice for any overfeed system.
To put it in other words, we design our plants so that we can fit all the liquid in the LP tank, incase the consumers need major service.
Mostly, getting all the liquid back to the tank is done by service personel from us or whatever other company is available at the time.
it is also safe for the onboard engineer to do this, close the pump inlets, shut of the pumps, have one compressor running in auto and our load controll system takes care of the rest.
The 80% Charge I said is also more like a rule of thumb :)
Lets say I have a system with 20 plate freezers, but the tank can only hold a charge for 18 of those (18 if the tank is topped off), I will then fill enough to run 15 freezers at one time, inform the ship owner and chief engineer that "your tank can only hold enough charge to run 15 freezers at a time yadda yadda yadda, live with it"
ofcourse there are some ships running with a 120% charge, cause the chief engineers are ordered by the ship owner to charge more *****, to get more consumers running...
But when we charge, we charge just so that we can fill the tank to the brim without getting liquid back to the compressors.
if that made any sense :)
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by Andy
We use filters in the range 40 to 100 micons range, quite fine really:D I favour big bore long drop legs, put the surge drum on one floor and the pumps on the floor below with a straight line down into the pump (vortex breaker at the top of the pipe, ball valve at the pump, all say 6" on a 2 1/2" or 3" inlet pump.
Kind Regards Andy:)
I always put ladies nylon stockings inside the pump outlet/ice filter (our pumps can handle the dirt, so we only have outlet filters :D brag brag brag :D), on new plants, and re built plants.
I supply the onboard engineer with some spares so he can change them if there is to much dirt, or if there isnt, I'll change them the next time they are in, I run the plant with the stockings for a minimum of a month, usually two months.
The reason for this is that you can run the plant with a bigger mesh filter afterwards.
but it's always embarrasing when you go to the store and stock up on nylon stockings like another perv :D
This one time I accidently bought ancle high when I needed thigh high stockings, and I had to go back to get the ones I needed... same very very handsome looking girl operating the register when I got there with my second armful of stockings.
Her: "Oh... I see you really like those"
(I turned lobster red in less than a second.. it was like *POOOF* I'm red)
Me: "oh.. hehe no, ummm filter... mesh and yeah, they... I use them... they are fine meshed... umm as a filter"
We use condoms to cover up the safety valve outlet when checking for small leaks in the safety valve, and one time we had a poor guy have to go to the store to get nylon stockings, condoms and dishwasher soap...
I'm just glad I wasnt that guy :D
oh, this should have been in the chit chat section, buy hey :D
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Re: Liquid Overfeed Systems
Quote:
Originally Posted by Tycho
if that made any sense
Perfectly...
BTW, do you have a preference on the color of the stockings you buy?....for filters that is.:D
I have used and recommend the condoms over the relief valve vent lines also. It sure does get a lot of comments when one valve is leaking.:rolleyes:
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Re: Liquid Overfeed Systems
guys do you know where i can buy equipments for liquid overfeed system online that has a brochure... nid help pls...
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Re: Liquid Overfeed Systems
Hi guys,
Anybody got any ideas or prices or website for Ebara Direct Fire CHILLERS-RAD-G028.
Could use any help.
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Re: Liquid Overfeed Systems
One location to find information on recirculation packages is to check out the Evapco website at evapco.com
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Re: Liquid Overfeed Systems
Hi corineramer,
What type of equipment are you looking for?
Pumps, evaporators, valves, pressure vessels, ???
If you can provide some more details, we can provide more information to help you.
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Re: Liquid Overfeed Systems
well US Iceman im just a student... we have a plate that we need to finish.. we're to design one utility of an ice cream plant and we picked the refrigeration system and we used the liquid overfeed system our proffesor told us to use that system... we dont have any idea where we could find all the equips that we need the eveporator, condenser,separator, ammonia pumps, etc.. we have a minimum capacity of 50 TOR... can u help me?? is there a site where they offer all of the equips?? we only need the brochure or specs.. thnx for replying we badly need help.. also 1 of our problems is we havnt been to an ice cream manufacturing plant we dont hav any idea what the machines look like inside the plant how they are arranged, that sort of thing... we need it for our plant lay-out...
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Re: Liquid Overfeed Systems
Hi, corineramer :)
follow this link and enjoy ;)
http://www.refrigeration-engineer.co...7621#post47621
Best regards, Josip :)
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Re: Liquid Overfeed Systems
Here is a link for evaporative condensers:
http://www.evapco.com/media/pdf/173B...Con-EngMan.pdf
Here is a link for liquid overfeed packages (vessel & pumps)
http://www.evapco.com/media/pdf/asme-recircular.pdf
Here is a link for the celing hung evaporators for the holding freezers:
http://www.evapco.com/media/pdf/nt-series.pdf
Here is a link to some ice cream production machines:
http://www.tetra-pak.com/ Look under the links for "Production".
Here is a link to some compressor information:
http://docnav.grasso-global.com/DocN...e/Screws_e.htm
Here is a link for control valves + other good information:
http://www.danfoss.com/North_America...+Selection.htm
That should keep you busy for awhile. :D