Pnumatic circuit


#1

hai iam working in automation project iwant clarification about pnumatic systerms am using one small size of tank pass through 1 bar air pressure in using pnumaticoperated valve and both end iam using air pressure gauge but both end pressure gauge can’t showing same pressure value its showing some value lesthen are grater then what is the problerm this how to solve this problerm.


#2

The only way there can be flow is when there is a pressure difference between 2 points. It is the pressure difference that ‘moves’ the medium.

So there is always a higher pressure upsteam and a lower pressure downstream.


#3

thanks your reply sir,
1 more dout about pressure calculation sir am using mitsubshi hmi and mitsubshi fx 5u plc pressure transducer 0 to 5 bar and 0 to 10 volt they are custumer request showing in hmi display in pa
(1 bar =100000 pa) custumer component leak range is setpoint 1 to 5 pa it is possible to detection of ok not ok cheking how to calculate ?
iam using just 10 v= 100000 pa calculation


#4

Leak testing is possible by charging a closed vessel to some pressure and monitoring the change in pressure but there are limits of usefulness.

A major limit is the resolution of the monitoring system for detection of the required minimum leak rate.

For instance, detecting a leak of one bubble (assume a bubble is 1mL for sake of argument) in a water submerged 100L vessel would require a resolution of better than 1 part in 100000 (1mL in 100000mL) because resolution is usually plus/minus some number of digits at the low end.

A pressure charged closed vessel is a closed system so Boyles and Charles’ Laws apply - the pressure changes with temperature. The change in pressure due to a low leak rate in a (relatively) large vessel would not be noticeable because the pressure changes due to temperature changes would mask the pressure change due to the leak rate.

Although a system might display an analog value to 5 or 6 digits (particularly those that work in floating point math), it does not mean that the low order digits are useable or that they are either precise or accurate.

For a 5 bar system to display a reading of 5000000 pa with any degree of accuracy or precision is not realistic with industrial grade instrumentation.

The best industrial pressure transmitters ar 0.01% accurate, which is 1 part in 10000, which is 2.5 ORDERS of Magnitude less than the 5000000 pa you are looking for.

At 5000 Kpa, an industrial analog transmitter with 0.1% accuracy should give a plus minus 5 Kpa reading. The question then becomes, how much a leak rate needs to be detected over what period of time to declare that the device ‘passes’? Just the cooling of a charge of a compressed gas or heating of a source of high pressure depressurized gas (like from a gas bottle) will be evident in a pressure change.

My personal experience is that leak detection via pressure charge is only good for rather catastrophic leaks due to production faults - bad seams/welds that bleed off pressure quite rapidly.


#5

Corrections from a north American who does not use Kpa routinely ( I did not catch the original post error: 5 bar does not equal 50000000pa; 5 bar = 500Kpa

For a 5 bar system to display a reading of 500000 pa (not 50000000) with any degree of accuracy or precision is not realistic with industrial grade instrumentation.

The best industrial pressure transmitters ar 0.01% accurate, which is 1 part in 10000, which is 1.5 ORDERS of Magnitude less than the 500000 pa you are looking for.

Using Kpa, then for 500 Kpa, an industrial analog transmitter with 0.1% accuracy should give a plus minus 0.5 Kpa reading on the display, which is reasonable.
The point being, that for a display to use pa units, the last two digits are garbage: 5000xx pa.
For a display that uses Kpa, 123.4 Kpa could be a reasonable value with a system capable of 0.1% accuracy.

The question then becomes, how much a leak rate needs to be detected over what period of time to declare that the device ‘passes’? Just the cooling of a charge of a compressed gas or heating of a source of high pressure depressurized gas (like from a gas bottle) will be evident in a pressure change.

My personal experience is that leak detection via pressure charge is only good for rather catastrophic leaks due to production faults - bad seams/welds that bleed off pressure quite rapidly.


#6

thank you so mutch ur reply carl_e


#7

carl_e thank you your valluable feedbacks…