Pulling faster vacuums

[Aranon]

Knowing that using time to measure a vacuum is like using a clock to measure weight, I am trying to pull micron vacuums faster.

Does any one know if using two new 6 cfm vacuum pumps would pull down faster than one new 12 cfm pump? I have heard 2 was better. If it is how do you hook them up. We are putting in 33 new systems and the line run is only 30 feet of 1 1/8" and 1/2" on a 4 hp system. It is taking hours to pull down to 500 microns and costing me lots of OT. I am using a new NRP 6 cfm pumps and hooking one on the roof and one down below with 3/8" hose and have the shrader cores removed. Still takes forever.

Would using two 6 cfm pumps be faster than one 12 cfm pump. Is there a better way to hook two pumps up? I don't mind hooking several pumps up if it would pull down to 500 faster.

Any suggestions. Any help. The OT is killing me. Please help if anyone knows. What is the best way to hook up multiple pumps if that is the way to pull it down faster.

Is one on the roof and one on the bottom fighting each other. Sould I have a vacuum trunk line and hook 2 or more pumps to a manifold with 3 tees? Please help.

Thank you,
Aranon

[Toosh]

Knowing that using time to measure a vacuum is like using a clock to measure weight, I am trying to pull micron vacuums faster.

Does any one know if using two new 6 cfm vacuum pumps would pull down faster than one new 12 cfm pump? I have heard 2 was better. If it is how do you hook them up. We are putting in 33 new systems and the line run is only 30 feet of 1 1/8" and 1/2" on a 4 hp system. It is taking hours to pull down to 500 microns and costing me lots of OT. I am using a new NRP 6 cfm pumps and hooking one on the roof and one down below with 3/8" hose and have the shrader cores removed. Still takes forever.

Would using two 6 cfm pumps be faster than one 12 cfm pump. Is there a better way to hook two pumps up? I don't mind hooking several pumps up if it would pull down to 500 faster.

Any suggestions. Any help. The OT is killing me. Please help if anyone knows. What is the best way to hook up multiple pumps if that is the way to pull it down faster.

Is one on the roof and one on the bottom fighting each other. Sould I have a vacuum trunk line and hook 2 or more pumps to a manifold with 3 tees? Please help.

Thank you,
Aranon

Hi Aranon, Have you ever thought on getting a 2 stage vacuum pump it might be a better idea. Google it and see what you can find

Toosh

[desA]

At what rate of vacuum pull-down does the system implode?

In other words, all good things must come to an end. Does the limitation lie in the ability of the vacuum pump to pull down, or in a safe pull-down allowing components to equalise & settle along the journey?

I know that on my systems, as vacuum is pulled, you can hear the system groaning a little, in the early stages.

[Gary]

Far more important than the pump CFM is the size of the hoses and fittings you are evacuating through.

Try breathing through a straw and you will get the picture.

[Aranon]

I am using 2 stage pumps. Right now I am using a new NRP 6 cfm 2 stage and a JB 6 cfm 2 stage. I am thinking of getting the new NRP 12 cfm if that is faster.

I was told that two 6 cfms were better than one 12 cfm. But I don't know if I am hooking them up right.

What is the best way. I am told by advertising from the different manifold/guage companies that using a 3/8" hose pulls down 4 times faster.

I am going to buy the Yellow Jacket Brute and replace the 1/4" fitting with 3/8" fitting. The Brute manifold using 3/8 pipe threads vs. the 1/8" pipe threads into the block like other brands. Then I plan to use all 3/8" hoses and use 1/4" to 3/8" adaptors on my Micron Guage and one the condenser. This way I am pulling all through 3/8" hoses with the only exception being my Micron guage (which reduces to 1/4" then back to 3/8") and the ports on the condenser. If the unit does not have a king valve, then I am using a shrader core remover with another 1/4" to 3/8" reducer.

My goal is to have everything at least 3/8" to pull vacuums if possible. I will try this and see if it pulls faster.

But where to hook the second pump. Inline, parallel or in series. One on the roof at the condenser and one at unit at the evap. Will I pull oil out of the other pump. Should I hook the up to a tee. Help. Anyone know what the best scenario would be.

Aranon

[Gary]

At what rate of vacuum pull-down does the system implode?

At perfect vacuum there is less than 15psi pressure differential. Systems do not implode.

[desA]

At perfect vacuum there is less than 15psi pressure differential. Systems do not implode.

Depends on the system, to be honest. Tube constructions are very strong under vacuum - plate surfaces are not. 15psi over an extended surface is a lot of force imbalance.

In a previous life in the petrochemical industry, I was warned about the dangers of pulling vacuum.

[Gary]

In 40 years I have never seen any part of any refrigeration system implode.

Possibly things are different in the petrochemical industry.

[desA]

^ I expect that the refrigeration systems are designed to withstand high pressures & are probably of pretty thick, robust construction. This helps. Good to know that no failures under vacuum have been seen.

The idea I was also trying to bring up was whether there was a suitable maximum safe rate of vacuum pull-down, which allows the residual stresses in the materials (put there during high-pressure operation), to slowly relieve themselves - preventing weld cracks & potential later leakers.

[desA]

An example...

[Aranon]

Ok, enough with the collasping my piping. If you think that is going to happen with a 12 cfm vacuum pump then I don't think you will be able to help me with the other questions.

Anyone out there know any thing about pulling micron vacuums and what the fastest way is with multiple pumps.

I know how to pull a vacuum, I know what hoses to use, I know you can't pull a micron vacuum through shrader valves. At least not in a day. I know what kind of pumps to use. I know about changing the oil. What I want to know what is the best sequence to hook up multiple pumps to pull a deep 500-400 micron vacuum the quickest. Any one out there know?
Aranon

[Aranon]

The only problem I know of using to large of a vacuum pump is there is a possibility of freezing any moisture that is in the system. But the ice would gas off with sublimation anyway.

Oh, I like the picture of the tanker. I think they used a 1.5 single stage pump on that tanker.

[nike123]

Check this PDF!
http://www.mediafire.com/?zmyztx5gnzm

Here is part of it:

Size of High vacuum Pump for Field Service Work

"There is no advantage in using a large pump for field service work. Experience is proving that a 3 CFM pump is large enough to service up to 10 ton refrigeration units. For larger units, an 8 CFM pump will get the job done as quickly as say, a 50 CFM pump."~SIC Pg. 43

The old rule of thumb which is the CFM Cubed = the size of the unit to be evacuated may be a little off, but this isn't definitive in the book. Suffice it to say that in residential work where the norm is someething less than 5 tons a 3 CFM pump is all we need and in Commercial work an 8 CFM is all we need. The secret, as we will find, is in the size of the hoses!

"In the language of vacuum engineering, this maximum attainable rate of gas flow (CFM), through a vacuum manifold at stated average pressure, is called teh "Conductance Speed" of the manifold."~SIC Pg. 44

The maximum rate of gas flow through a hose, when pulling a vacuum, is called the conductance speed. Remember that, we will come back to it in a minute. But first we need to establish the types of flow during the evacuation process.

There are three types of flow during the evacuation process:
1) Viscous (or Laminar) Flow
2) Intermediate (or Transitional) Flow
3) Molecular (or Diffusion) Flow

How do you know what stage you are in? It's pretty easy actually!

Laminar Flow: Where the pressure, measured in Microns, is equal to or greater than the numerical value of 100/d, where d is the inside diameter of the vacuum line in Inches.

Molecular Flow: Where the pressure, measured in Microns, is equal to or less than the numerical value of 4/d, where d is the inside diameter of the vacuum line in Inches.

Transitional Flow: Exists between these two limits.

We now begin to see that the INSIDE DIAMETER of the hose has a great deal to do with the conductance speed of your vacuum manifold. The goal is to transition from Laminar Flow to Molecular Flow in the least amount of time. All else being equal, smaller diameter hoses will greatly increase the time required to pass through all the transitions of gas flow. How much of a difference we will discuss next.

On Edit:I failed to mention the actual Micron levels where we achieve the different flows, it is pretty interesting actually. With 1/2" hoses we are still in Laminar Flow until we reach 200 Microns, Molecular flow starts at 8 Microns and Transitional is, of course, in between. With 3/8" hoses, Laminar down to 266.6 Microns and Molecular at 10.6 Microns. We never really get close to Molecular Flow in our work, but the longer you can stay in the Laminar Flow region the faster the evacuation will go.

Exactly how much does the size of the hoses effect conductance speed? The easy answer is BY A FACTOR OF 4! Which
doesn't mean very much unless I add this bit of information; for every 1/8 Inch increase in hose size! That's right, for every
1/8 Inch increase in hose size the conductance speed is increased by a factor of 4!
It is interesting to note that:
"The conductance speed of 1/4" O.D. refrigeration tubing is too small to be used as a connecting line to a system; so we will
not even discuss it. Never use it if you can avoid it as it is too costly in excessive pump-down time."~SIC Pg. 60
This book was published in 1959! In 1959 we knew that 1/4" hoses were inadequate to use for system evacuation, WHY DO
WE USE THEM NOW??? Stop it!
A few examples:
3/8" raised to the 4th power = .009
1/2" raised to the 4th power = .036
.036/.009 = 4 times (duh!), here you can see that by increasing the hose size by 1/8' increases the conductance speed by 4
times.
5/8" raised to the 4th power= .095
.095/.036 equals an increase in conductance speed of 2.6 times that of 1/2" hose and 10.5 times that of 3/8" hose!
What about 1/4" hose?
1/4" raised to the 4th power = .001 (.009765625)
How much faster is 1/2" than 1/4" ?
.036/.001 = 36
1/2" hose has 36 Times the conductance speed of 1/4" hose!!! IOW it is 36 times FASTER!
I have heard this many times from people:
"My boss tells me to pull a vacuum for 20 minutes." Well, if they were using 1/2" hoses that would proly be long enough!
But using 1/4" hoses it will take much longer to reach the proper vacuum level!
Summary:
Stop using small hoses and big pumps! Start using smaller pumps and BIGGER hoses. It is faster, less work (smaller pump is
lighter), costs less in the long run

[Tesla]

From experienc on chillers I found using 2 pumps was definatly slower than using one big one (same size/rating as yours) I spoke with an oil consultant who advised me that oil starts to decompose below 300microns. I had a special 5/8 stainless corrugated tube made attached to tee with 1/2 lines going to each side of the system. The biggest thing was, for the volume of chiller to change the oil once or twice durring evacuation and the quality of the vac oil. If it is cold I reccomend using IR heating. You could also run a fan to create a little vibration which helps noncondensables to come out of the oil faster. Not many techs know how to maintain a vac pump properly so follow the vac pumps manual for a longer lasting pump - they are expensive. One other thing is to check your pump before use - a good pump would pull 12 - 25 microns and a bad one would only pull 50 microns. This might be a little overkill for the size system you are working on.

[HallsEngineer]

Bigger hoses and if you wish to use two pumps please section the system off as one pump can pull through the other at low vaccuum. CFM really only matters when your hose size gets large like 1" and above as the vaccum pump can easily handle anything below this. Schraeders are the vaccuums worst enemy. Any restriction means pressure drop means not as low as you should be and puts more strain on your pump and takes longer. Also anyone who vacs through their manifold should be shot. The orofice inside those manifolds is tiny.

[nike123]

Also consider purchasing this kit:
http://www.appioninc.com/downloads/f...t_Brochure.pdf

[Aranon]

Thanks Nike123. I knew someone out there could help me. I downloaded the PDF and it is really interesting. It amazes me how many people work in refrigeration and have absolutely no idea of what they are really doing. I remember when I took a refresher course for my state licence the instructor asked, " How many of you are hooking up your hoses to the shrader ports of you equipment and pulling micron vacuums down below 500 when you pull vacuums. About 3/4 of the class raised there hand. Then he held up a shrader valve remover with an access port on the side and asked how many or you have one of these? About 10 people raised their hand.


Then he said, well 10 of you might be telling the truth. Then he asked how many of you carried Micron Guages/meters on their truck and only 3 or 4 raised their hand. He then said, theres only 3 or 4 in here that I would even let look at my equipment.

That's when he said, " I can't believe that I got over 150 people in this class about to get their Texas State Refrigeration License and they don't even know how to pull a proper vacuum and much less know if they did or not. He said people, you can not pull a proper deep vacuum through a shrader core. At least not in the time you willing to be at the job. Remove the cores.

That's when I bought my first Micron Meter and valve core remover tool. I took me longer to learn about that big black hose on my 4-port guages that everyone took off and replaced it with a 1/4 standard hose.

Thanks for the info. I have always heard that a 3/8 hose pulls 4 times faster than a 1/4 but have never seen anyone explain why or how. Thank you again.
Aranon in Texas

[Tesla]

Guys I seriously think using any gauges on evacuation is a big mistake it's another place to leak. Can't see any referance to use of ballast - it should be open untill a vac of around 1500 microns then closed. I bought a set of refco gauges whith a snapon vacum roughing gauge (class 1 = accuracy within 1% full scale deflection). And yellow jacket has more and better data on pulling vacumes including schrouder removal/superheat tool.

[nike123]

Guys I seriously think using any gauges on evacuation is a big mistake it's another place to leak.

Can't see any referance to use of ballast - it should be open untill a vac of around 1500 microns then closed. I bought a set of refco gauges whith a snapon vacum roughing gauge (class 1 = accuracy within 1% full scale deflection). And yellow jacket has more and better data on pulling vacumes including schrouder removal/superheat tool.

Tesla did you read that review and Apion brochure at all, or you just expressing your beliefs:

Gas Ballast
On Page 74:
We begin to discuss the Gas Ballast; first it's definition and then principle of operation.
"Gas Ballast is a technical term inherited from Germany where it was first applied to rotary high vacuum pumps. Within
narrow limits, its purpose is to prevent vapors from condensing within the pump during the discharge stroke, or action
[rotary].
In our field service work its use is limited because large systems might contain more water than the gas ballast can handle
quickly. Generally it saves time to change the small quantity of pump oil rather than wait for the gas ballast to free the oil of
excess water. However, we will explain gas ballast because it is available for all sizes of high vacuum pumps." ~ sic
And because it is a mystery to most people!
Definition:
Ballast: The state of equilibrium for that portion of air that is taken in during the intake stroke and exhausted during the
exhaust stroke. Let's say the vacuum pump takes in a displacement of air that is 100% saturated with water vapor; as the air
enters the pump the water vapor will remain as a vapor (not condense). The "State of Equilibrium" which keeps water in its
vapor form is what is known as "Ballast".
Gas: Free air is introduced in the outlet (compression) stroke to help maintain this 'Ballast'; as free air is a gas, we have the
term 'gas ballast' meaning that a 'gas' is introduced into the 'ballast'. IOW, you are gassing the ballast in order to keep water
vapor from condensing.
But why...?
This is how your oil wets out. During the exhaust stroke, the saturated air is compressed which causes the water vapor to
condense. The pump must overcome atmospheric pressure, plus valve spring pressure to exhaust the air. By opening the gas
ballast we allow atmospheric pressure to rush into the exhaust void, thereby lowering the compression ratio and, hopefully,
keep the water vapor from condensing.
Using the Gas Ballast: It is best to open the gas ballast after the pressures are less than 10 mm or 20 mm (10,000-20,000
Microns) and then close it after the rough vacuum has been achieved. The book doesn't say but I close mine around the 2-
3000 Micron mark.
Maintenance of a High Vacuum Pump
You can read the next three pages for yourself (pages 78-80 actually), but here is the condensed version:
1) CHANGE YOUR OIL! Often...
2) Choose a pump that is easy to break down and clean
3) Use a good Micron gauge to know when your oil has wet out
4) CHANGE YOUR OIL!

[Peter_1]

Aranon, I haven't read all the replies - too much work for the moment - use indeed two pumps but try to install them as far as possible from each other For example: one on the compressor and one at the evaporator or condenser.
If you vacuum very large systems like supermarkets, then you will see that the point the most far away from your pump will lag. So if you install also there a pump, then you counteract the pressure drop over the long copper. Even a copper line provokes pressure drop while vacuuming

Pumping down always with short 3/8 hoses (you can buy 1 way manifolds. Try to pull through 3/8 fittings you soldered on the systems.

Fresh oil in the pumps.

Double or triple vacuum you system: first cycle, vacuum far beyond the limit you need, rinse with OFN till you break atmospheric pressure, re-vacuum and break eventually a second time with OFN. You then dilute the remaining air and moisture which is easier to pull down.

Copeland heats up their windings with a controlled DC current to heat up the oil (don't know the values for this) and speed up the vacuum process. You can use

The difference between a 6 CFM or 12 CFM isn't that important for your system, it's more the final vacuum you can reach with it which is far more important.
If you calculate once your content of your present system, you will see that even the smallest pump will empty it within a minute or so. Then you don't pump volume flow but you"re only trying achieving the desired vacuum.

A dump question: we use Pa, how much Pa is 500 micron

[Tesla]

Hi nIke 123
Yes I did read it in full, thats why I replied. How long would these gauges hold a rating of 20 microns in service? What would one require compound gauges for durring an evacuation process - one that I can think of, just to make sure we havn't got a big leak on a vacuum fitting. My compound gauges were fairly leak proof untill a few years went buy but then...

[nike123]

My compound gauges were fairly leak proof untill a few years went buy but then...

Then you should change O-rings in them.

Only leak proof solution is if you braze your vacuum pump to system, but that is impractical.
If you keep your tools in top condition, then I don't see reason to not use this setup if it is rated to 20 microns.
One advantage is that is 4 times faster than YJ evacuation kit due to use of 1/2" hose and bores in gauge.
We are in money making business and time is money.

[Thermatech]

I dont do much evacuation these days
but
I used to find the following with large systems.

Most vac pumps have at least one 1/4 connection & one 1/2 or 3/8 connection. I have one Watsco vac pump with three 1/4 & one 1/2 connection.

So if you use a short hose lines with a built in ball valve & use shreader removal tool you can connect the vac pump direct to the system with 1, 2. 3, or even 4 hose lines without any manifold gauges.
then
You can still hold the vac in the system & disconnect the vac pump by using the built in ball valves on each hose line.
then
You can deploy standard triple vac procedure with OFN.

Cutting out the maniford gauges helps.
Using multiple direct hose line connections to the system helps.
Using shreader valve core removal tool helps.
Using OFN triple vac helps.

[Silhouette]

I use an 8CFM pump with a 7/8" manifold connected to 4 3/8" bore hoses. This will usually do the trick on large supermarket packs overnight!

My spare is an 8CFM pump with two 3/8" flare connections using the 3/8" bore hoses again.

[wandowski]

i have invested over the last year in a yj 6cfm,plus a superevac manifold with 2 3/8 lines with shutoff valves which connect either to 1/4 fittings or 1/2 fittings,and sit my torr gauge on top of the tree,remove all the cores and takes no time atall to pull a deep vacuum,

[RANGER1]

To add to everyone elses comments its also faster if the initial leak test was performed properly and at the highest test pressure possible for the equipment . It then has to hold that pressure for a period , if it does'nt there is a leak .
If there is an open drive compressor it has to be isolated during vacuum til the system reaches desired vacuum , then vac it out .
It also takes time , but you don't have to watch it .
When you ara putting system together continually seal things up so no moisture can enter pipes + equipment as otherwise you then have to get it out later .

[coolments]

Hi Aranon

Those gauges proposed by nike look just the ticket but going back to your original post that over time is killing you waiting for the vacuum.
Not sure on the logistsics of the job or your location to it but are you not tempted to leave the vac on over night, after all 4 hours overtime pay = 6 hours during normal working hours, it may pay to go back rather than sitting and waiting.

Off topic from your question but something I want to say.

I remember asking the guy that trained me when i was an aprentice 'how long does it take to vac a unit down" his answer was "as long as takes" and how true is that, following with "what most people dont realise is its not just about creating a vaccum to get rid of air etc its about hitting one and holding it, its also about creating one to lower the boiling point of water in pipework to below the current ambient temperature so it will boil any moisture inside and be able to be removed by the pump".

I know you already know this but some readers may not. I have a chart somewhere for this but cant put my finger on it at the mo so heres a link to Robinair

http://www.robinair.com/acsolutions/...acuum.htm#eff1

[HallsEngineer]

I think you have a leak.

[wandowski]

when evacuating a system where do have your pump?higher or lower than the system or service ports?my pump seems to leave alot of oil from the pump in the lines,dont know if its due to the position of the pump beening higher

[nike123]

when evacuating a system where do have your pump?higher or lower than the system or service ports?my pump seems to leave alot of oil from the pump in the lines,dont know if its due to the position of the pump beening higher

No, that is because of improper turning off of vacuum pump.
You need first to isolate pump from system than introduce air in vacuum pump (if pump doesn't have check valve or isolation valve) and then turn off pump.

When you turn off pump, vacuum in system or gauges or hoses is grater than in pump, and that pressure difference suck oil from vacuum pump in to lines.

[wandowski]

thanks,have recently purchased a yj vacuum tree with to 3/8 hoses for faster/deeper vacuums,now when reach vacuum level i close the valve off on tree and watch for rise and then close valve on pump,

[nike123]

thanks,have recently purchased a yj vacuum tree with to 3/8 hoses for faster/deeper vacuums,now when reach vacuum level i close the valve off on tree and watch for rise and then close valve on pump,

Close valve on pump first than on vacuum tree, than turn off vacuum pump.