volume versus pressure
volume versus pressure
(OP)
We have a vacuum device that is specified in l/min from our design centre, but our line testing unit is measuring in mmH2O.
Is there a conversion between these two units?
We are seeing drift in the pressure measurements that give the impression that the units are out of spec on the low side, however, if I send some sample failed units to the design centre, the l/min measurements are all in spec.
The pressure measurement system is using differential pressure. The voltage and speed of the motors has been checked and these are in spec.
What, if any, outside influences could be causing the variation?
Colin.
(The design centre's response to this problem was, 'buy a different tester that measures l/min', which, while it is a solution, isn't likely to happen unless the current tester explodes.)
Is there a conversion between these two units?
We are seeing drift in the pressure measurements that give the impression that the units are out of spec on the low side, however, if I send some sample failed units to the design centre, the l/min measurements are all in spec.
The pressure measurement system is using differential pressure. The voltage and speed of the motors has been checked and these are in spec.
What, if any, outside influences could be causing the variation?
Colin.
(The design centre's response to this problem was, 'buy a different tester that measures l/min', which, while it is a solution, isn't likely to happen unless the current tester explodes.)





RE: volume versus pressure
RE: volume versus pressure
Colin
RE: volume versus pressure
It is very similar to specifying where you are on earth by giving an Easting and a Northing co-ordinate. What your design centre is doing is giving you only the Easting, which means you could be anywhere between the North Pole and the South Pole on that line of longitude. Not very helpful if you are trying to plan your wardrobe.
They must specify the pressure that goes with the l/min value they have given you, and you need to measure both to be sure that you are achieving the desired performance.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: volume versus pressure
Any thoughts on possible external influences on the pressure readings. The sensor assembly is an Omega PX275-05D1, with the readings being taken off the low side of the differential sensor.
Colin.
RE: volume versus pressure
If there are differing flow rates then pressure will fluctuate downward each time flow is required and will increase to normal when the flow requirement ceases.
An Accumulator, (Vacuum Chamber, the bigger the better)in the line can reduce the pressure fluctuations but will not eliminate them. Locate the Accumulator as close as poossible to the reason for the fluctuating flow.
Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com
http://www.fluidpower1.us
RE: volume versus pressure
RE: volume versus pressure
This is assuming that the design center has all the specs and knows what needs to be tested and what the specs are. Having worked in several design centers, I know this is not always the case. If the design center is measuring leak rate but is supposed to be measuring pressure, tell them to buy a new tester.
RE: volume versus pressure
In the tester, we connect the drill bit end of the unit, via some tubing, to the low side of the sensor. We then run the unit, this sucks air from the drill end, through a filter, then out the side of the unit.
The test cycle goes as follows.
Run units for 10 seconds, measuring pressure and amps. If pressure is too low, unit is rejected. Repeat 5 times.
Uses a dc motor rotating at 21 - 24 k rpm, to spin a fan, to get the airflow. We buy the motors in, and they are already run in.
Colin.
RE: volume versus pressure
Ideally, measure differential pressure across a nozzle with known characteristics. Make the nozzle part of your test appartatus.
RE: volume versus pressure
Then set up a test rig with 2 orifices, one to simulate the loaded filter, and one with the water gauge connected across it to measure the flow rate as described by The Tick.
Jeff
RE: volume versus pressure
flow and speed are related to each other by the formula of Bernouilli which sounds
P = Rho*g*h + 1/2*Rho*v²
Here the speed component is v²/2g if you devide all the terms by Rho*g and gives you meters H2O
Success
Kind Regard,
Chris
RE: volume versus pressure
Hope ColinScowen has his problem resolved.
RE: volume versus pressure
always feels good helping brothers in arms
Kind Regard,
Chris