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Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/22/2013 7:49 AM

Good day

We need to monitor the pressure of reciprocating engine power cylinder

The pressure inside the power cylinder fluctuating from 200 PSI to 700PSI

Can I use normal pressure gauge? Or it will break

Is there permanent pressure gauge designed for this situation

Best regards

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Guru
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#1

Re: pressure gauge for fluctuation pressure 700-200 psi

04/22/2013 7:54 AM

To measure the maximum pressure, configure a bit of pipe onto the equipment, fitted with an isolating valve, a non-return valve and the pressure gauge. Make sure there is a snubber on the gauge inlet connection. Open the isolating valve slowly and, after a number of revolutions, the gauge will read something approximating to the maximum pressure.

The volume of the pipe, valves and gauge needs to be "small" in comparison with the volume of the cylinder for it to be accurate. If it isn't small, use P1V1/T1 = P2V2/T2 to apply a correction.

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#2

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/22/2013 9:50 AM

Wait a minute. How can this engine work if the pressure never falls below 200 PSI?

And you will not be able to read a pressure gage at any rate. The needle will be constantly moving fast enough so as to be invisible.

You need a pressure transducer and a chart recorder.

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#3
In reply to #2

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/22/2013 10:46 AM

Unless the mechanism is turned over slowly, by hand/wrench, I don't think it is a pressure gauge application.

If I recall correctly, Nyquist's theorem says the sampling rate has to be twice the maximum process frequency to avoid aliasing. But a Nyquist minimum sampling rate doesn't guarantee catching peak values.

A 600 rpm reciprocator would need 1200 samples per second to avoid aliasing; probably 10x that sample rate, or 12,000 samples per second to get a reasonable wave form.

12KHz is a very fast pressure sensor and probably needs an oscilloscope's sampling rates, since paper/paperless chart recorders typically are a max 10 points/second, with one brand's high speed option at 50 points per second.
That's OK, low end o-scopes like the Rigol are less expensive than a recorder nowadays.

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#4
In reply to #3

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/22/2013 10:31 PM

A factor of 60 slipped in here: 600 RPM 2 stroke has a Nyquist limit of 1200 samples per Minute or 20 samples per second. For 10X that's a 200 Hz sample rate. Still too fast for a Bourdon tube gauge or paper recorder. Easy with a PC and a strain gauge based transducer. If we truly needed 12 kHz, a piezoelectric transducer and a charge amp would be my initial approach.

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#5

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/22/2013 11:55 PM

In the chemical and petroleum processing industry the most frequent methods to handle this situation is to use either a glycerin filled gauge or a snubber.

The interior of the filled gauge is filled with glycerin and this acts as a dampener on the needle by being much more dense than the normal air in an unfilled gauge (this resists the frequent movement of the needle as with pulsations). Filled gauges are easily identified by the liquid within them and usually a rubber disc/plug on the top to facilitate filling it or topping it off.

The snubber is short piece of pipe that has a small orifice in it that restricts the upward pressure pulses and restricts the flow out or the gauge on the downward pulses. There is sometimes a small chamber included in it to further dampen the pressure pulses. These are usually very effective, especially when combined with the filled gauge.

Another thing to do is to buy quality gauges and if the material of construction is compatible with the measured material use a gauge with a stainless steel bourdon tube (based on my own experiences). The stainless is much stronger than the usual brass/bronze. Also use larger gauges (for example a 4" or 6" filled gauge instead of a dry 2-1/2" gauge) since the needle is larger and resists the momentum more than the dry smaller gauge.

Both filled gauges and snubbers are available at most local supply houses and also McMaster-Carr (3820K37 for example) and Graingers .

Please note- these suggestions are based not on highly scientific formulas but on personal experiences and the past practices of many engineers and tradespersons out in the processing "trenches", along with a lot of common sense from those people.

Good Luck, Old Salt

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#10
In reply to #5

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 5:15 AM

A snubber, only, is fine if the average pressure in the line is wanted. The idea of including a non-return valve in #1↑ is to prevent reverse flow through the snubber so that the gauge reads only the maximum pressure. Would this work?

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#11
In reply to #10

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 7:56 AM

Although the original poster did not seem to specify what type of pressure he was looking for I interpreted it as the average pressure, the type most frequently wanted in the process industries. If I was wrong please forgive me.

Yes, a check-valve in the supply line to the gauge will soon indicate the maximum pressure incurred. The only problem might be, with a non-leaking system, is how do you relieve that pressure within the gauge when the unit is shut down? Theoretically the gauge would read the highest pressure in the life of the system. By-pass solenoid valve, etc.?

Good Luck, Old Salt

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#6

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 12:28 AM

You need a pulsation dampener gauge from MD TOTCO division of National Oilwell they have an externally adjustable pulsation dampener built into the gauge that will suit your needs. They may also be obtained with with an analog electrical output that you may use to record the pulsation rate and range to any device that will read resistance/voltage.

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#7

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 12:56 AM

Hey.... you just forget about everything...Just install a pressure gauge which is filled with Glycerin and can read the maximum range.I am sure your problem will be solved.

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#8

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 1:14 AM

Which Pressure-- Peak Max.-- Minimum at exhaust?? For reliable Investigation?

Each Cycle? All cycles?

Gauge - any gauge will fail to give you These. Will in fact break down .

You need PiezoElectric sensors and signal processing .

Ask Texas Instruments . They will have such IC+Signal Processor combos.

You will need cooling the pressure pulses between the cylinder and IC

Best done with a hydraulic oil filled diaphragm seal .

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#9

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 2:49 AM

if you want to fit a gauge i would recommend a glycerine filled gauge fitted with a viscous damped movement and an internal restrictor/snubber all of these will dampen and slow down the movement of the pointer as its pressure increases and also protecting the gauge thus increasing longevity of the gauge. if you wish to monitor amximum pressures you could also fit a max indicator pointer which is dragged up the scale as pressure increases and remains there until you manually reset it to zero. You can also get max/min pointers which will do the same but show maximum and minimum pressures obtained.

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#12

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 9:43 AM

Measuring pressure that oscillates can be done if you use some very old techniques:

1.- Depending on the length of the cycle you can install either a needle valve to dampen the measurement or

2.- Fill the face of the pressure gauge with a dampening fluid or

3.- Buy a pressure dampener like a syphon or specialty valve.

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#13
In reply to #12

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 9:51 AM

this is what i said, we manufacture gauges daily to withstand pressure surges and drops from low pressure upto high pressure (4000bar) as used on water jetting systems which are constantly being surged up and down

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#14

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 9:55 AM

if the gauge is likely to see heat, it would probably need to be all st.st. construction but you could not glycerine fill it as this would blacken and turn to toffee (ok if you have a sweet tooth) so silicon oil fill, inlet restrictor, viscous damped movement, even an external damping coil if you want an all singing all dancing unit, but this then gets expensive.

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#15

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 5:02 PM

Thank you for your feedback Let me till you more details We have v8 reciprocating engine running @200 rpm which is used to drive reciprocating compressors The temp inside the power cylinder sometime above 600'C Can the pressure gauge filled with glycerin handle this? Because I'm thinking what is the best cheap method

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#16
In reply to #15

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/23/2013 8:45 PM

Unless there is some reason that you couldn't use it in your particular system, the gauge could be located far enough away from the cylinder that a small, but appropriately sized, heat exchanger could be put between the cylinder and the gauge. Thermal transfer oil (Thermanol is one brand) may be necessary as the cooling liquid on the primary heat exchanger which would then be cooled in a secondary heat exchanger cooling with water or some other readily available and replaceable liquid. Since there is very little flow through the pipe/tubing this system would not have to be substantial i.e. the longer the pipe/tubing probably the less cooling has to be used. In fact the installation of fins on the outside of the tubing prior to the heat exchanger(similar to a baseboard heating section) might also reduce the size of the system, just don't touch it or stand near it!

This is based on the hot gasses cooling the longer time they are in the tubing. Very little flow, and that is back and forth, once the tube is filled with the compressed gas being read.

This way of cooling is similar to how samples of boiler water are taken from a high pressure steam boiler for analysis. If they weren't cooled prior to removal it would evaporate as steam when it left the boiler and no sample would be obtained.

Good Luck, Old Salt

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#17
In reply to #15

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/24/2013 2:49 AM

on certain high temperature applications we have in the past manufactured a heat dissipating coil, which works the same way as old salt states, but does not need to be sited so far away. glycerine is no good at all at 600'C, you would need to research what damping liquid to use, i do know they use a liquid to damp exhaust pyrometers which i have seen ranged at 650'c, but i have never looked into this, try Sika thermometers.

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#18

Re: Pressure Gauge for Fluctuation Pressure 700-200 PSI

04/29/2013 4:37 PM

you need to refer manufacturer's catalog for the Peak Pressure Limit of the gauge and do not exceed that limit. Working pressure levels are well defined for every gauge and peak limit are not for regular use as they may cause irreversible damage.

Shyam

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