Get a compressor for Christmas?

[Tracy]

Just FYI, air isn't free, even when you squeeze your own. If you are buying a compressor to save a ton of money, you will be disappointed. If you are buying for convenience, you will be pleased.

 

[NAM001]

You are not going to have to go to 50 amp. 30 should be plenty. I have my electric capitano on its own breaker so the freezer in hte garage does not conflict.

ok it's one phase and I already have a 30amp service in garage but I could easily go up to 50 amp with out upgrading house service.

 

[Octopusprime]

Just FYI, air isn't free, even when you squeeze your own. If you are buying a compressor to save a ton of money, you will be disappointed. If you are buying for convenience, you will be pleased.

It it is not really about saving money... I understand there is maintenance costs. There is a conveyance part because right now if 4 of us go diving we have at least 10 tanks. If we want to dive somewhere that does not have fill service we can only dive one day and then on the way home we have to try to make it to a shop before they close to dive the next day. If I had my own I could just go home refill and leave the next day... Not to mention we are starting to buy gear for students. Which means another 10-20 tanks...

 

[NAM001]

Please explain how bpr is not reauired for ballance. Clearly I need to learn something here. Every compresser has an optimum final presure where it runs like a singer. its all about force. force of 1st stage presure and its piston area (constant once started). the force of the 2nd stage pressure on its piston area. (constant once started) and the force of the 3rd/final stage presssure on its area which varies with the system back pressure. the bpr is to maintain a constant back pressure on the 3rd stage. Without it,, it will rattle and pump like a one legged man in a relay race. Too low a setting and it will vibrate and too high it will vibrate. So please educate me on the matters of ballance of force. I am not rying to be a jerk.. You appear to be so convinced that your position is correct that i am giving you the opportunity to explain to my understanding. There has to be something I am missing. And are you refering to only the rix design or does this apply to all compressors and crankshaft/wobbleplate styles.

Regards

I'm interested where you got that misinformation from. Always interesting from an engineering perspective to learn how miss information gets into the main stream.

The Axial design of a Rix has three stages the first two developed pressure and are in constant ratio to the final stage discharge pressure.

Without a BPR fitted the final stage pressure is only compressing to the same as the cylinder pressure being filled and if empty can cause damage to the floating piston as with any other brand or design.

The back pressure regulator on all compressors irrespective of brand or design does two jobs non of which in any way controls balance.

The BPR allows primarily a buildup of pressure in the final stage to hold the floating piston against the rod to reduce chattering as the rod under no load hits the bottom of the piston and the lack of back pressure throws the piston up onto the head
The rattling that can be heard on start up on all compressors irrespective of brand.

The second value of a BPR is in filtration when as pressure increases the water separation effectiveness is increased reducing the water condensate carry over onto the filter chemical thus with less water to adsorb the filter chemical last longer.

The balance on a Rix is due to the weight of each piston and the "Throw" of the swash plate balancing and cancelling each other out, As the 3 pistons are each of a different size with the first stage being the largest a counter weight is used fitted to the crankshaft fan end to aid balance.

Further a solid steel driven pulley at the rear is bored with 4 19mm holes PCD to counterbalance the radial movement of the piston against the axial rotation at the driven belt end.

The BPR is not used or required for balance and I got socks for Christmas. :depressed: LOL

Iain Middlebrook

 

[iain/hsm]

Please explain how bpr is not reauired for ballance. Clearly I need to learn something here. Every compresser has an optimum final presure where it runs like a singer. its all about force. force of 1st stage presure and its piston area (constant once started). the force of the 2nd stage pressure on its piston area. (constant once started) and the force of the 3rd/final stage presssure on its area which varies with the system back pressure. the bpr is to maintain a constant back pressure on the 3rd stage. Without it,, it will rattle and pump like a one legged man in a relay race. Too low a setting and it will vibrate and too high it will vibrate. So please educate me on the matters of ballance of force. I am not rying to be a jerk.. You appear to be so convinced that your position is correct that i am giving you the opportunity to explain to my understanding. There has to be something I am missing. And are you refering to only the rix design or does this apply to all compressors and crankshaft/wobbleplate styles.

Regards

1. A BPR by itself does not affect or alter balance. The back pressure mealy reduces piston chatter and it takes very little for the piston to stop chattering a few pounds pressure will do for a floating head piston. The fact your filling a big cylinder is the reason you fit a BPR or the time taken to created sufficient head pressure on the final stage piston would be measured in minutes rather than in 20- 30 seconds and in that time wear and damage is amplified. causing both piston ring damage and "washboarding" of the piston liner

This is not the same as the optimum BPR pressure setting for maximum water separation measured in 1500-3000 psi.

2. However the term balance needs also to be expanded as there are a number of balance considerations in a compressor design, some of which are balancing forces.

Rod load over piston area over pressure is I think what your describing

Your "Runs like a Singer" comment is I think the mechanical balancing of the moving parts that can induce vibration described in earlier post.

3. However by your description I think your also questioning the balancing out of the rod loading.

4. As far as rod loading is concerned they also should be balanced in that each stage however different the piston diameters the rod loading or pressure over surface area ideally should be equally balanced in a good compressor design, in that each rod gives and equal rod loading on the crankshaft and con rod bearings.

5. Take the Rix SA-6 again the three piston rod loadings are designed to be balance at 3000 psi. By balance I mean that the rod loads are equal or balanced out a 3000psi using a 3", 1,25" and a 0.56" 3rd stage piston diameter

Now if you increase the discharge pressure to say 5000psi you alter these three "balances" just as much as you would filling from empty pressure to full.

First the rod loads increase 1st @707.26 lbs 2nd @770.55 lbs 3rd @ 1241.89 lbs
You also need to calculate the rod loads a TDC top dead centre, BCD bottom dead centre and with convectional crank designs with the rods also at 90 degrees to the
crankshaft.

Also the balance of the interstage pressures 1st @100.11 psi, 2nd @ 628.22psi, 3rd at 5000psi affect rod load for a given area

Then also adiabatic temperature balance (before cooling) 1st stage @ 493.5F,
2nd stage @447.95F and 3rd stage 538.1F at a discharge pressure of 5000psi

6. But there are other balances such as thermal balance, that is the heat of each stage requiring adequate cooling prior to its approach into the next higher stage
This is approach temperature balancing. This needs balancing with the heat dissipation capacity of the cooling coils, heat exchanger, Fan RPM, number of fan blades and fan tip angle etc.

7. Then there is the thermal balancing of the gas being compressed say from Hydrogen to Argon, lightest to heaviest gases and all in between. As well as "Blow-By" altering the mass flow of gas by the blow-by or leakage of the light gasses past the piston stroke under compression, leaking past and into the crankcase compensated for by either a larger piston diameter, gas packing etc

8. Finally you have the unbalanced forces and moments usually calculated on larger pistons when you would have primary, secondary and couple forces to calculate based on the mass of the piston, the stoke of the piston and the RPM

This is most of what I would consider balance in a compressor design, Not all of which affect vibration. Iain Middlebrook

 

[NAM001]

Thanks , since you put it wht way i guess i was right.

1. A BPR by itself does not affect or alter balance. The back pressure mealy reduces piston chatter and it takes very little for the piston to stop chattering a few pounds pressure will do for a floating head piston. The fact your filling a big cylinder is the reason you fit a BPR or the time taken to created sufficient head pressure on the final stage piston would be measured in minutes rather than in 20- 30 seconds and in that time wear and damage is amplified. causing both piston ring damage and "washboarding" of the piston liner

This is not the same as the optimum BPR pressure setting for maximum water separation measured in 1500-3000 psi.

2. However the term balance needs also to be expanded as there are a number of balance considerations in a compressor design, some of which are balancing forces.

Rod load over piston area over pressure is I think what your describing

Your "Runs like a Singer" comment is I think the mechanical balancing of the moving parts that can induce vibration described in earlier post.

3. However by your description I think your also questioning the balancing out of the rod loading.

4. As far as rod loading is concerned they also should be balanced in that each stage however different the piston diameters the rod loading or pressure over surface area ideally should be equally balanced in a good compressor design, in that each rod gives and equal rod loading on the crankshaft and con rod bearings.

5. Take the Rix SA-6 again the three piston rod loadings are designed to be balance at 3000 psi. By balance I mean that the rod loads are equal or balanced out a 3000psi using a 3", 1,25" and a 0.56" 3rd stage piston diameter

Now if you increase the discharge pressure to say 5000psi you alter these three "balances" just as much as you would filling from empty pressure to full.

First the rod loads increase 1st @707.26 lbs 2nd @770.55 lbs 3rd @ 1241.89 lbs
You also need to calculate the rod loads a TDC top dead centre, BCD bottom dead centre and with convectional crank designs with the rods also at 90 degrees to the
crankshaft.

Also the balance of the interstage pressures 1st @100.11 psi, 2nd @ 628.22psi, 3rd at 5000psi affect rod load for a given area

Then also adiabatic temperature balance (before cooling) 1st stage @ 493.5F,
2nd stage @447.95F and 3rd stage 538.1F at a discharge pressure of 5000psi

6. But there are other balances such as thermal balance, that is the heat of each stage requiring adequate cooling prior to its approach into the next higher stage
This is approach temperature balancing. This needs balancing with the heat dissipation capacity of the cooling coils, heat exchanger, Fan RPM, number of fan blades and fan tip angle etc.

7. Then there is the thermal balancing of the gas being compressed say from Hydrogen to Argon, lightest to heaviest gases and all in between. As well as "Blow-By" altering the mass flow of gas by the blow-by or leakage of the light gasses past the piston stroke under compression, leaking past and into the crankcase compensated for by either a larger piston diameter, gas packing etc

8. Finally you have the unbalanced forces and moments usually calculated on larger pistons when you would have primary, secondary and couple forces to calculate based on the mass of the piston, the stoke of the piston and the RPM

This is most of what I would consider balance in a compressor design, Not all of which affect vibration. Iain Middlebrook

 

[iain/hsm]

Thanks , since you put it wht way i guess i was right.

I prefer to discuss in general terms of "what is right" rather than "who is right"
The Rix has a number of outstanding advantages over a conventional compressor,

The BPR also has its advantages.
But using a BPR pressure setting (too low of too high) to control vibration is not one of them. Iain Middlebrook

 

[NAM001]

I dont believe I said using too low or too high to control vibration. I said too high or too low back pressure causes vibration and there is that backpressure that makes it run like a singer. Most manufacturers recommend a set backpressure. I think rix says 1900 or something like that. But it does not matter I will most likely be running mine while you are repairing yours.

I prefer to discuss in general terms of "what is right" rather than "who is right"
The Rix has a number of outstanding advantages over a conventional compressor,

The BPR also has its advantages.
But using a BPR pressure setting (too low of too high) to control vibration is not one of them. Iain Middlebrook

 

[iain/hsm]

I dont believe I said using too low or too high to control vibration. I said too high or too low back pressure causes vibration and there is that backpressure that makes it run like a singer. Most manufacturers recommend a set backpressure. I think rix says 1900 or something like that. But it does not matter I will most likely be running mine while you are repairing yours.

No. What you actually said was, and I quote:

its all about force.

No it is not, it is about balance

(constant once started)

No it is not, it is increasing until final pressure is reached.

the force of the 3rd/final stage presssure on its area which varies with the system back pressure

No it does not. The force on the 3rd stage piston varies with the downstream filling pressure. NOT the back pressure setting
How the heck do you get to make a fill
The BPR setting is fixed for optimum water separation

the bpr is to maintain a constant back pressure on the 3rd stage

No it is not it is to maintain a minimum back pressure on the 3rd stage NOT CONSTANT

Too low a setting and it will vibrate and too high it will vibrate

No it will not

Look you use the terms "Believing and thinking" a lot and these are wonderful concepts, however neither of them will do you any good with compressor design,
or with Rix, Your call. Iain Middlebrook

 

[NAM001]

Ian here is the exact line i posted Too low a setting and it will vibrate and too high it will vibrate.

Nerxt eaual force allows equal ballance. To maintain a constant force on the 3rd stage and resulting ballance you put a bpr on it to keep the 3rd stage at its ballanced pressure despite what the tank psi is.

the final 3rd stage pressure varries with the filter/tank pressure unless you put a bpr on the 3rd stage to keep it constant which keeps the compresser in ballance because of equal force on all stages. I will even go with equal angular force.

I think any futher discussion is futile as you either do not understand mechanics or do not understand what you read. We will not find common ground.

No. What you actually said was, and I quote:



No it is not, it is about balance



No it is not, it is increasing until final pressure is reached.



No it does not. The force on the 3rd stage piston varies with the downstream filling pressure. NOT the back pressure setting
How the heck do you get to make a fill
The BPR setting is fixed for optimum water separation



No it is not it is to maintain a minimum back pressure on the 3rd stage NOT CONSTANT



No it will not

Look you use the terms "Believing and thinking" a lot and these are wonderful concepts, however neither of them will do you any good with compressor design,
or with Rix, Your call. Iain Middlebrook