discharge muffler

[cretan]

I recently worked on a 3 door freezer.404a ref.semi herm.the previous compressors valves went and the cylinder walls were scored.When I replaced the compressor,I took the discharge muffler off.My questions are what does the muffler do and will the system work properly with-out it?Thanks!!!!!

[US Iceman]

A discharge muffler on a refrigeration system works on a similar principle as mufflers on cars and trucks.

The muffler reduces sound noise and high frequency vibration.

The baffle plates in the muffler are selected and positioned to dampen the vibrations which result from the pistons moving up and down (or similar effects in a screw compressor with the rotors and discharge port area).

Imagine the following: throw a rock into a lake. Then when the waves start to return to you, throw another rock into the waves.

What you will see is one set of waves impacting on the first set of waves. In effect, one wave tries to cancel the effect of the other.

This does not greatly affect the system performance or capacity, but it may allow the vibration levels to increase. You would need to verify if the effect is bothersome, or potentially trouble.

[Samarjit Sen]

The discharge muffler is to absorb the sound created by the movement of the pistons. If the same is removed, it has no effect on the performance and efficiency of the system.

[smpsmp45]

I think it is a must to reduce the vibrations. We also did similar exercise earlier on similar units & leakages never stoped untill we went back with the muffler in position

[tadipatrir]

I think discharge muffler in a compressor is always associated with some pressure drop at the cost of reducing noise. Hence once discharge muffler is removed it will slightly improve the capacity. Noise level also will depends on the application of the compressor. For HBP, it will be high.

[US Iceman]

There is some associated pressure loss when a muffler is used. However, since the muffler is installed on the discharge of the compressor there is a minor increase in power input. Capacity is hardly affected at all.

If there are sufficient levels of vibration causing leaks, then there are some serious issues that need to be resolved. The use of muffler to prevent this only shows how difficult it can be to properly design piping systems.

[cretan]

thanks for your help everybody!!!!

[Samarjit Sen]

Vibrations caused in the pipe line can be due to various reasons. Mostly it is due to improper installation of the compressor which could also be due to not using proper foundation blocks, improper pipe layout, not providing supports at appropriate distances.

Muffler is basically to dampen and absorb the sound of compressors internal noise. By not installing them it does not in any way effect the performance.

[TXiceman]

Technically, it is not noise it is reducing, but pressure pulses. Most mufflers an expansion area and a choke. The choke or orifice, if properly designed can and will provide some recovery on the pressure losses.

I had a customer leave the choke plates out when they rebuilt a 5h series Carrier compressor. The result was he broke the discharge line about a week later. When we discover the "unused parts" we repaired the suction line and reinstalled the choke tubes. No more broken lines.

On another job with a competitors custom built unit, the unit was built cheaply with out an oil separator or a discharge line muffler and they were cracking joints in the discharge line with regular frequency. I installed a discharge line muffler and solved the problem.

On a smaller recip, the pressure pulses are not as bad as the larger recips. But you can still get into trouble. An oil separator will help, but not necessarily as well as a muffler.

The design or discharge mufflers or volume bottles on large recips is a real science. They also put them on the suction of larger machines.

You can see the effect on the muffler if you take vibration reading down stream of the compressor. if you manage to design or build a system that the discharge line is tuned to a resonance frequency and length of the pumping frequency, it can not only be heard but felt.

I would not delete a discharge muffler as when properly selected, the line loss in minimal.

Ken

[Samarjit Sen]

Thank you Ken,

I have seen very few installations where the mufflers have been used. If using the muffler is an advantage to the plant, then one should install the same.

The working of an oil seperator is quite different from that of a muffler. The oil seperator separates the oil particles that that are entrained in the gas and returns the same to the compressors. It does not remove 100% of the oil, but it does remove about 70 to 80 %. I am always using an Oil Seperator with all my plant. They are mostly of Temprite and the coalescent type.

[D.D.KORANNE]

Muffler is installed to remove pulsations gernerated by pistpn compressors.Usually, on high speed recip comp with short discharge lines. Oil separator & muffler normally are to be avoided togethe although functions are different.

Koranne

[TXiceman]

The oil separator does tend to attenuate the pressure pulses to a small degree and the general purpose is not the same as a discharge muffler.

A good coalescing oil separator should stop about 99.9% of the droplet oil on screw compresors. The vapor state oil can not be stopped unless you go well beyond normal coalescing type separators. To get it all you need to start looking at carbon bed absorption vessels.

You can help the excessive oil carry over to some degree by using the proper oil with a higher vapor pressure so that less oil is vaporized at the discharge temperatures.

Ken

[Samarjit Sen]

Good Morning Ken,

Thank you for your suggestions. We are generally using reciprocying compressors and in all my plants am installing oil seperators. I am interested in knowing more about the carbon bed absorption vessels. Could you please provide me with some links to the same.

Thank you Ken

[TXiceman]

A number of companies build CBA units. If is a high dollar separator to stop vapors and toxic fumes. problem is you will need to install two in parallel and switch vessels while you regenerate the other one if you are to run 24/7.

Basically to regenerate the carbon bed, you have to heat it to drive what it has absorbed.

This is typically not used in closed loop systems. Where I have used them are on open loop systems such as gas compression or vapor recovery with screw compressors where the outlet stream would be contaminated with the slightest amount of oil.

Do a Google and see what you find in your area.

Ken