Small 4 stage reciprocating compressor for fueling vehicles 1

[hook111]

Hook111. 4 stage small cng reciprocating compressor for vehicle fueling
I am in the process of testing a small 4stage natural gas compressor that we have been trying to build for the past two years to fuel our vehicles with. With many design changes the past two years trying to build a small compressor to reach a fueling pressure to 3600 psi at a rate of 6Nm3/hr to 12Nm3/hr. The problem I am now having is in the 4th stage the wear between the piston and cylinder and not being able to develop pressure more than a limited number of hours. After around 200 hours the blow by leaking around the piston keeps it from coming to max. pressure of 250 bar to only around 100 bar, only reaching max. (250 bar) for the first 200 hours or so. Then it get progressively worst from there.

I am looking for help in finding a cylinder material (not steel/metal) that would wear much better with durability that would reach closer to 3-4,000 hours. The piston material also needs to be such that excessive wear doesn't cause the compressor to lose pressure. Maybe some type of composite material other than traditional hard steel. The wear between the piston and cylinder come quick in it's present form.

3rd stage piston rings have also been a problem with blow by but I am testing new materials to see if they will help solve the problem .

One of our biggest problems have been the 4th stage check value. The flat disc type with a spring wears fast causing leaks after a very short period period of time. Again maybe poor material but the design seems to wear out quickly. I don't think a stronger spring would help, the disc still wears and isn't durable. I haven't been able to find help in finding any type of overhead valves for this size or type of compressor that will reach 250 bar pressure.

Resources for these problems have been very difficult to find for this compressor and application. That's why I am appealing to anyone who might have any suggestions or direction that might help me with this compressor. I probably need to start over again but don't want to lose all the time put in the last two years.
If anyone could help me with a material for the 4th stage cylinder and a check valve that would work I would be most grateful.

Thanks to anyone with help in advance.
Hook111

3rd stage piston rings are also a problem but I am testing different materials now hoping to find some that are also durable .

One of our biggest problems is the check valve also in the 4th stage. The disc type we are using wears fast causing leaks after a very short period. I don't think a stronger spring would help, the wear would still occur. I haven't been able to find help in getting the correct overhead valves for a small compressor of this size to reach 250 bar.

I haven't been able to find resources for this type or size of compressor either so that's why I am appealing to anyone that could help with information or direction, especially on cylinder material and or check valve source.

Thanks in advance to anyone that can help with any of these questions.
Hook111
howardhooker@aol.com






















I haven't been able to find help in gettin the correct overhead check values for a small compressor to reach 3600 psi. I am at a stage that I probably should start over again but hope that with some help I might be able to get a compressor working after so much testing and work.

I haven't been able to find a small compressor of this size in the market place,

 

[Montemayor]

Hook111:

Why does your post take up so much space?

12 Nm3/hr (approx. 7 Scfm) is not a small capacity. It is a microscopic capacity. 100 Scfm is a small capacity - so you have a "jeweler's" size of machine that you are trying to work with.

3,600 psig discharge is nothing extraordinary. This is done everyday in many industrial applications and so also the compression of natural gas to 250 barg which is not a big deal as reciprocating gas compressors go - even if you don't tell us your suction pressure or compression ratios.. Your troubles with your machine have to originate with either your experience level, materials of construction, mechanical design (piston speed, valve velocities, rod loading, piston and cylinder design, piston ring design, etc., etc.) or your machining capabilities and results.

Answers to your questions may lie in the developed knowledge and know-how of experienced manufacturers - such as Arrow Engine Company in Tulsa, OK. Go to

http://www.arrowengine.com

and download their flier #VRCCNG-ML-F. There, you will find a complete listing of the design and materials they use to compress natural gas to 4,500 psig.

 

[zdas04]

I've asked management to delete the last 3-4 ft of his post. I'm betting he went to sleep on his keyboard.

The OP's pressures and flow rate made me think of a Scuba air compressor. Seems like a better place to start than with a Hoerbinger catalog and a lathe.

I figured he was probably pulling on a house supply downstream of an ounce regulator and going back to CNG pressures. I've heard of people trying this, and I keep waiting to hear of it blowing up a home.

David