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Frequently Asked Questions
Personal Air Sampling Pumps
Piston
calibrators for use with the industrial hygiene sampling
pumps have inherent flaws.
- The
piston must return to the bottom of the flow cell to
repeat a flow reading. To do this, an internal valve
closes, placing an insertion pressure spike into the
flow stream. (a quote from a piston calibrator manufacture)
This blocking of flow disrupts personal air sampling
pumps.
- The
glass walls of the flow cell will condense moisture
(like a window on cold winter day in a home) and the
piston cannot move.
- Piston
drag from its weight can influence the true pump reading.
Adding more backpressure at calibration time will provide
inaccuracies to the readings.
- Piston
leakage is always a concern, but is not a factor with
a soap film. Self-test must be built into piston calibrators
to check against this failure.
Why do these pumps require constant flow ?
Battery voltage dropping during the sampling day or sample filter plugging can slow the pump. Better pumps have some kind of circuitry to monitor the pump flow and to maintain it's flow within +/- 5% for the day. There are pumps still being manufactured today without constant flow. The BUCK pumps are rated at +/-3% to the days run.
Do other manufactures have one hour rechargeable pumps and why is this feature so desirable
No! Fast charge batteries arrived on the market in the mid 80's due to advanced chemistry in the cell. They are heavily used in various consumer markets such as video cameras and the hobby industry. The BUCK pumps have the fast charge type batteries. This feature is extremely popular with sample takers for the reason that most wait until the last minute to prepare to sample. It requires about 16 hours to charge competitor's pumps. Some Hygienists want to sample the second shift on the same day. A fast recharge allows this to be a practical consideration without having to bring extra pumps and batteries.
What is back pressure and why is it important to personal air sampling pumps ?
Back pressure is the measurement in inches of water of the resistance to flow causes by the filter media. For example, the standard 37 mm cassette with a 0.8 micron pore size filter will create a back pressure of 5 inches water pressure at 2.0 liters per minute (LPM). At 3.0 LPM the pressure is 15 inches. The higher the pressure the more the pump has to work and the more current is drained from the pumps batteries. Other than battery drain is the consideration of the pump's mechanical ability to pull against the resistance. Generally, the pumps are rated in maximum inches of water pressure. But unless a flow rate is given with the pressure it is relatively meaningless. The BUCK pumps use stainless steel valves and can pull up to 60 inches depending on the motor and flow.Why do some pumps require a "Pneumatic Test Kit" to check back pressure correction of flow ?
These pumps use a pneumatic regulator to maintain constant flow. If adjustment is off, the pump will fault off, causing a loss of the days sample. The BUCK Pumps monitor the pumps strokes and controls any deviation to flow by computer control. Features such as auto-restart or pump stop if the filter falls off, are not available to these manufactures because of the analog/pneumatic regulation.What is meant by "shielded" battery powered powered personal sampling pump?
This is referring to Radio Frequency Interference (RFI) and Electro Magnetic Interference (EMI). This can disrupt a pumps flow by introducing strong current and voltage to the circuitry. The BUCK pumps are 100% digital and are inherently immune to this effect and does not require "shielding".
Why is the auto restart from flow blockage such a popular feature of the BUCK Pumps?
Other pumps shut down to protect the battery and circuitry and cannot restart due to lack of intelligence in analog pumps. With computerized control of the pumps, restart can be programmed at specified intervals until the original flow is recreated. Thus, the elapse time of the sample is accurate and the hygienist is further assured of being able to complete a credible sample.
Why do some pumps have an outside filter which must be cleaned frequently
Pumps are used in dirty areas and if allowed to run with the hose off dirt can clog the internal pump valves. In theory, the sample filter should be stopping all the dust and therefore a filter is not needed. However, in reality, if the hose comes loose (or if the sample filter falls off) the pump continues to operate sucking in all the dirt.
The BUCK pump stops running and displays "FILTER IS OFF". This stops the pump from drawing dirt until the operator can reattach the hose and restart the pump by pressing ENTER. In addition, a small replaceable inline filter is inside the pump and can be easily removed for occasional cleaning.
Is there consistency in filter cassettes from box to box or cassette to cassette ?
The variations in filter material is great. The technique of using a sample or "dummy" filter to calibrate the pumps air flow can lead to errors of 10 to 25%. Because the actual filter used was not measured for flow, this could cause it to be void in a Court of Law. The porosity of the filter material is a lower priority for the manufacturer than the purity and pore size precision. Hence, filter manufacturers don't grade the filter for flow (back pressure).