How A Oil Flooded Rotary Screw Air Compressor Works

Screw Air Compressor

All right well I’ve made a few explanations on these rotary screw compressors but I’ve

never really explained how they work to people that are in the field and there’s

not a lot of people in this field so I finally found a situation where it’s not

noisier than hell and I could kind of talk a little bit so I think this would

be a good opportunity first off we’ll start out with this tank right here

which is known as the oil reservoir or the sump tank it’s purposes are to hold

the fluid and it’s also a little small little air reservoir for the controls

and stuff of that nature just so we have a place to build air

pressure inside the system so basically the oil is used for three things in a

rotary screw compressor one is lubrication the next is cooling and the


other is ceiling or lubrication so basically what you have here is a

helical cut rotary screw compressor it’s got helical rotors in it it’s kind of

like what’s that a supercharger if you will oil is injected into this point right

here and there’s some small orifices on the bottom of the housing right here

which basically shoot the oil into the rotor housing and which gives you your

ceiling so then what we have once the compressor is turning is a discharge of

air and oil that comes through what’s known as the discharge line right here

and enters into the sump tank and it looks like it just goes right in the

side of that tank but there’s actually a baffle inside of the tank and basically

what happens is the discharge of air and oil is separated through gravity in the

oil falls to the bottom and the air oil mist goes to what’s known as a separator

element and that is what is housed in this flange on the top so this

particular unit has dual separation and these are what’s known as the scavenger

lines they go to the bottom of the separator element you can see these

stainless lines right here they go to the bottom of the separator element

which has a pan on the bottom of it and basically this is distributed to a low

point of low air pressure point inside the pump or it sometimes goes back to

the inlet under a vacuum situation and that’s where the oil is returned so

that’s what keeps the oil in the compressor otherwise it would go

downstream although you got to keep in mind all rotary screw compressors were a

little flooded rotary screw compressors for that matter

all will pass a little bit oil downstream alright so once the

compressor is up and running it starts to develop air pressure and we have

what’s known as the heat of compression and that’s where the cooling comes in

with the fluid so basically what happens is as the temperature rises inside of

the compressor itself it’s sensing it in this thermal valve right here and this

is a fluid diverting valve it diverts the fluid from either the cooler or

around the cooler and bypasses the cooler till it gets up to about oh about

one hundred seventy five hundred eighty degrees somewhere around there and

that’s a normal temperature on a rotary screw compressor will be about a hundred

degrees over ambient and then of course this being our main fluid line going in

we filter the fluid I know it’s upside down in most cases

but it actually still works the same way this is an air-cooled unit and so it’s a

fan cooled and inside here there is actually two coolers there is one for

the air side so it would be an Africa ler and then one on this other line here

is the oil cooler line two kind of designs with rotary screw compressors as

one is load on load and the other is modulated this machine is modulated and

basically it’ll match the demand for the plant air pressure providing you don’t

drop or use more air than what the capacity the compressor

here we have all the controls like I’d mentioned this one is why Delta start as

you can see with the three starters right here it has it basically a start

and run configuration I can’t stand it but it is what it is any why delta start

has got to be a load to start so on these rotary screw compressors when you

start them up especially on these american-made machines they want to make

air right away because the inlet valve is wide open basically so what we do in

this situation here is we’ve got a little pressure reservoir right here you

can see the pressure on that listen for a fill gaze it doesn’t look so good so

it just houses pressure here and if you were to break the line to the inlet

right there you would have air pressure not just keeping the inlet valve closed

for starting purposes only and this is our regulator to modulate

the compressor to proble the air to meet the air demands and then basically we

have a full load solenoid valve here if we want to take in excuse me it’s the

load/unload solenoid valve I make correct this is the full load solenoid

valve if we want to get this machine to run in sequence with another machine and

get this machine not to modulate and run wide open this valve comes into play

although it’s add some problems crap inside here and the guts are missing and

we’re not sequencing it so here we are on the top of the sump tank

or the air reservoir whatever you want to call it for oil reservoir rather

there is a spring-loaded check valve that all the air goes through it’s

called a minimum pressure check valve but it’s set for about 60 psi and it’s

designed so that you start the compressor up and there’s no air

pressure in the plan it will maintain 60 pounds of its internal pressure it’s

because used for lubricating the pump and there is no oil pump here so we have

to have at least a minimum of probably 20 pounds 30 pounds of pressure just to

move the oil like I said I think I just got done replacing the motor here this

is why Delta start and I don’t deal with too many of these and I actually have

the coupling element just assembled right now because I’m a little bit

concerned that when you start this if it’s not wired right from the factory

it’s going to try to go the direction it’s supposed to go and start and then

when it goes to run it might have the tendency to go backwards so it’s bad

enough that happens with the motor – let alone the pump so I have this all loose

right now and the coupling is out out of it at the moment so it’s got to get her

back in the room and I’ll get it running and get a explanation of it running and I’ll kind

of be about it thanks for watching guys all right one the motor failed that took

out these two contactors right here and it was a costly costly costly

endeavor not for me but for the end user and what I got right now is I don’t have

any power out here except for what I got here I got this little inverter right

here I’m right by the my vehicle by the van or by the compressor rather the

contactors are replaced by an outside contractor so I just wanted to make sure

that these things are going to be alright so I got some temporary power

hooked up here with a little circuit breaker gimmick right here this thing

works awesome for like testing coils and anytime you got a situation where it’s

blowing to control fuse it’s so easy just to use this and just disconnect

coils until you find the problem at least that’s what I found the best so

any rate I’m just going to kind of dry fire this thing starting here at least

see a guy down got a good display here so everything

should be good let’s see here we go like one contactors buzzing a little bit

that’s going to shut right down on a little some pressure because it thinks

it’s running what a day.


Source : How a oil flooded rotary screw air compressor works

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