Ella,

You have an open ended quuestion with no answer as

it all depends on the size of the reciprocating compressor and its power demands during a loaded and unloaded state.

You will have to start from the beginning and

determine what power is required by the compressor -this is easily calculated by determining the shaft speed of the given compressor at the stated revolutions per minute on the name plate.

You must then go to the NEMA frame size for that motor to determine the proper size/voltage/amperage for the reciprocating compressor.

Reciprocating compressors run at a lower revolutions per minute than screw or vane compressors and they are powered through a V belt and pulley set up as the prime mover /electric motor operates at a faster revolution per minute than the compressor with the larger diameter pulley driving the reciprocating compressor shaft. ■

Ella,

What you apparently need is additional compressed air storage as you can not make your compressor rotate faster and expect it to work properrly.

With AC power in Canada being sixty cycle why are you telling me you have fifty cycle?

Are you sure your three phase power is not 460-480 volt? If your voltage and amperage is not correct you will suffer line drop problems and the related consequences.

Alternate current volatages run 110-115, 220-240, 460-480, 600, 1000, 4000 13,800 34,500 115,000, 230,000, 675,000, 715,000.

The reciprocating compressor can only go so fast in revolutions per minute and it will fail other wiseas it is not designed to go faster simply because it is timed to rotate at that speed through the crank shaft and pistons.

Does the air compressor in question have an intercooler?, it may be plugged and if so it will need to be replaced. ■

Ella,

You have not stated whether this compressor is a radial compressor or what work you are doing with the compressed air.

Are you draining the air out of the storage tank regularly? it should be done everyday to the point that all the compressed air is drained from the tank and in the process all the moisture wiill drain away-water tanks a lot of compressed air power away if it is not drained from the air tank.

Please check the name plate on the compressor

and the electric motor the name plates will have all the relevent information on them for the electric motor such as RPM @ stated amperage and voltage and the compressor RPM and psi as far as what it is capable of-does the compressor have an

INTERCOOLER? this is very important.

Again it is important to remind you that the reciprocating compressor is only capable of one speed and it will not go faster with out destroying it. As I said earlier the motor is probably driving the compressor through a v belt pulley with a reduction in rpm from the electric motor through the v belt pulleys.

You should not change the v belt pulleys either as it will also change the delivered revolutions per minute of the electric motor as it will change the revolutions per minute of the compressor and it will not last very long. As I said before you need storage capacity, If you buy a bigger air tank to run in parallel with the other tank it will reduce the load on the compressor

Adding compressed air storage tankage is the only viable alternative in your case as you do not have a screw or vane compressor.

This can be done with an adequate sized tank to regulate flow to your process.

If your process requires more air you may need to purchase a bigger compressor in the long run anyway. ■

Ella,

Assume nothing,

you still have not told me if it is a radial piston compressor or vertical piston or what your are using the compressed air for.

Contact the compressor manufacturer before you do anything!!!!

If you need a bigger compressor buy one as this is the only real way to do this since a change over to 60 cycle power from 50 cycle stil requires a huge amount of work-I do not think your local electrical supplier will do this willingly with out you commiting to having your own transformer farm and a set of regulating transformers. Its a lot of work for one old air compressor that you could tie into your air system as an additional air source. ■

Dear Ella,

The formula for a piston compressor is :

Power = N = n/(n-1) * Q1 * p1 * ((p2/p1)^((n-1)/n) ¡V 1)

in which:

N in Watt

Q1 = 0.008424 m3/sec

p1 = 100000 N/m2 (absolute)

p2 = 900000 N/m2 (absolute) (8 barg)

n is the compression exponent (polytrophic) and is k = 1.4 for adiabatic compression.

In your existing case, there has to be also a efficiency factor incorporated.

Assume efficiency eta = 0.8

Then the consumed power by the compressor at 8 barg is then 3.22 kW

From the compressor data and using an adiabatic compression the motor is oversized already.

The electric motor can run on 480 Volt ¡V 60 Hz (says the nameplate)

The consumed current will then be the same as the Volt/Hz ratio is the same.

The same current means the same torque.

Increased rpm (1500 „ 1800) at constant torque means higher power.

If the compressor is running on 1800 rpm and at 8 barg,

then the consumed power is 3.864 kW and the electric motor

can deliver 1800/1500 * 4.17 = 5 kW at 480V ¡V 60 Hz

No problem on the electric side, when running at 480 Volt / 50 Hz.

But since you plan to run at 5 barg, the required power is only 2.96 kW

To achieve the 1800 rpm in Europe (400V/50Hz), you might need a Volt-Hertz regulator,

capable of converting 400V/50Hz into 480V/60Hz.

When running at 8 barg and 1800rpm with the Volt/Hz regulator, then the compressor requires 3.864 kW at (400V-50HZ) .

The electric switch gear should be OK.

(it is made for a 4.17 kW electric motor at 400V-50HZ)

Also check, whether the compressor can run at 1800 rpm, which would be normally the case, otherwise that compressor could not be sold to the US market.

Cost wise, it should be investigated whether a new compressor is feasible, taking into account

the present condition of the existing compressor.

Based on your info, problem solved.

best regards

teus ■

Dear Ella

N = n/(n-1) * Q1 * p1 * ((p2/p1)^((n-1)/n) - 1)

Any good school book or manual about thermo dynamics.

Laws of Boyle , Gay Lussac , Dalton , Poisson , Carnot , Stirling and all those illustrius man.

My school book is in dutch

best regards

teus ■

Teus Tuinenberg's comments always help. It takes some brains to be able to read a schoolbook in Dutch. ■