Is a Pumped Gas Monitor Right for Your Application?

Is a Pumped Gas Monitor Right for Your Application?

Gregg Bako | Thursday, January 11, 2018

Is Using a Pumped Gas Monitor Right for Your Application? - Ever since workers began using electronic gas detectors, they have used instruments with pumps. Nevertheless, exactly when and how pumps should be used is still a common topic, even today. Many people believe that every gas monitor should have a pump. They feel that without a pump the gas monitor is less accurate, slower to respond, and simply doesn’t detect as much gas. While having a pumped gas monitor does not mean its more accurate, quicker to respond, or able to cover more area around you, it will make performing certain tasks remarkably easier and safer. 

Why Use a Pump with a Gas Detector?

Pumped gas monitors allow you to easily pull the air from an unknown and potentially toxic or combustible atmosphere to your location so that you can view the monitor’s results in an area that you know to be safe. Pumps literally keep you out of harm’s way. Once you’ve assessed the air sample using a pumped gas monitor and confirmed it is clear of any toxic or combustible gases, you can enter the tested area and perform any work that needs to be done there.

Pumped gas monitors help to keep you out of
areas where potentially harmful gases may be lurking.

Often times, you will have a vessel that is not very tall, but may span a distance of 30 feet or more. In this type of confined space entry, a pump with an extendible probe allows you to slowly advance into the space with the probe ahead of you ensuring that the atmosphere is safe prior to entering further. Other times, the vessel may be tall and narrow, requiring an entry from above. In this instance, using a pump and sufficient tubing will allow you to check from above that the entire vessel has been completely emptied of any hazardous gases prior to entry. With both of these examples, you are allowing the pump and sampling equipment to pull the air to the monitor prior to entry, making the operations safer.

We’ve seen how having a pump on a gas monitor can make operations easier and safer; however, having a pump does not increase the range of detection or the effectiveness of the gas monitor. The gas monitor’s sensors will still only detect the gas that they come in direct contact with. Having a pump on a gas monitor does not increase the amount of gas the sensors see. Rather, the pump allows you to test the atmosphere at a distance from the monitor. Therefore, if you place two instruments next to each other and one has a pump with no tubing attached, it will not detect the hazardous gases any faster than the unit without the pump, and both units will read the same.

Why Not Use a Pump?

What is the downside of always using a pump? While the gas monitor will detect gas in the same manner whether it has a pump on it or not, a monitor with a pump will certainly be larger and heavier. Also, the pump will use some of the instrument’s battery, resulting in a shorter run time for the overall instrument. Since operators typically wear a gas monitor their entire workday, which could extend to twelve or more hours, having a gas monitor that is small, lightweight, and runs the entire shift is critical. Most people would agree that it is better to save the pumped monitor for where it is absolutely needed.

Other Things to Consider When Using Pumps

Once you have decided that a pumped monitor is needed for your tasks, you will want to make sure you have any other accessories to effectively use and protect your pumped monitor. If you’re doing a horizontal entry or using the pump to check areas that are difficult to reach, you will want to use a probe. This may be a lightweight polycarbonate probe, an extendable stainless steel probe, or perhaps a probe designed to withstand high temperatures. If you are doing a vertical entry, you are going to need some tubing. Commonly, you will see urethane and Teflon-lined tubing. Urethane tubing is suitable to sample gases with the exception of chlorine, chlorine dioxide, hydrogen chloride, and volatile organic compounds (VOCs). Chlorine, chlorine dioxide, hydrogen chloride, and VOCs can be absorbed by urethane tubing, leading to inaccurate readings. For this reason, Teflon-lined tubing is recommended for use with these gases. Any time you are using a pump with tubing, it is important to allow enough time for the gas sample to travel the length of tubing and diffuse into the sensors. A good rule of thumb is to allow two seconds for each foot of tubing, plus two minutes for the sensors to read and stabilize. That means if you have 30 feet of tubing attached to your pump, it will be three minutes before you will get readings from the gas at the end of that tubing. Another important tip when using a pumped gas monitor is to use a dust filter and water stop at the end of the tubing or probe. In addition to preventing damage from dust and debris, it will prevent liquid from being pulled into the pump motor should the end of the tubing get dropped into any liquids.

Whether you are working in a water treatment plant and verifying that a tank is free of gases prior to its maintenance, or checking for leaks among a number of hard-to-access valves and piping in a refinery, using a pumped gas monitor will keep you out of harm’s way. For personal monitoring applications where remote sampling is not required, consider sticking with a non-pumped monitor.

Want to switch back and forth between a pumped instrument and non-pumped instrument on the fly? Check out our blog post on using a slide-on pump.