Air Pumps and Accessories for the LI-830, LI-850, and LI-7000

The sample cells of the LI-830, LI-850, and LI-7000 gas analyzers must be continually flushed while making measurements. The system time constant (T), a measure of how quickly the system responds, is determined by the cell volume and flow rate through the cells:

1‑1

The list of parts on the next page can be used to make a simple air flow system to move sample air streams through these analyzers. Parts available for sale through LI-COR are listed, as well as alternative vendors. Note the following precautions when designing your air flow system:

  • Always install an external air filter into the sample air stream before it enters the analyzer. Failure to do this will lead to contamination of the optical path.
  • Pressures of 15 kPa or more above ambient can cause damage to the source and detector windows. The safest mode of operation is to pull air through the optical bench.
  • Devices such as valve-actuated rotameters and regulator valves can be used to reduce flow rates.

The LI-830 and LI-850 analyzers are available with a built-in pump. If you want to add the pump as a retrofit option, we offer 800-910 pump kit, which provides flow control and diagnostics integrated with the gas analyzer. The pump installs in the analyzer case, and it is powered through the analyzer power supply. It provides a fixed flow rate of 0.75 liters per minute (lpm). If your instrument is not equipped with the built-in pump, you can use any pump with a maximum flow rate of 1.0 lpm.

Example #1: Built-in Internal Pump

Figure 1‑1. The built-in pump operates at negative pressure, drawing the sample through the optical bench.

The internal pump is positioned downstream of the optical bench and thus, it provides negative pressure on the system. There is no need to use a regulator, exhaust vent, or flow meter in this configuration.

Example #2: External Pump with Positive Pressure

Figure 1‑2. A user-supplied pump on the inlet side of the analyzer pushes air through the optical bench. The regulator valve should be adjusted to achieve the ideal flow rate by allowing air to escape the pressure vent.

An external pump upstream of the analyzer is ideal when dealing with large volumes of incoming air. This configuration is less prone to leaks because it uses positive pressure. Be careful with very humid air, because the positive pressure can cause water droplets to form.

Example #3: External Pump with Negative Pressure

Figure 1‑3. A user-supplied pump on the outlet side of the analyzer draws air through the optical bench. The regulator valve should be adjusted to achieve the ideal flow rate by allowing air to be drawn through the pressure inlet.

An external pump downstream of the analyzer is ideal for injection measurements and small-volume measurements. This configuration is more susceptible to the effects of a leak because it uses negative pressure, but it eliminates the risk of excessively pressurizing the optical cell.

Flow Rates

Table 1‑1. Acceptable flow rates for the LI-830, LI-850, and LI-7000 gas analyzers.
Model Min. Flow (lpm) Max. Flow (lpm)
LI-830 and LI-850 0.25 1
LI-7000 0.25 ~50

Plumbing accessories, filters, and scrub tubes available from LI-COR

Description   Part Number
Bev-A-Line tubing 1/4” OD, 1/8” ID 15 meter roll 8150-250
Straight union 300-3123
Right angle union 300-03125
Y-Union 300-03367
T-Union 300-07385
Regulator valve 300-10471
Filter assembly for use with the LI-830, LI-850, or LI-7000 9967-008
Filter for use with the LI-830 300-01961
Scrub tube assembly 9960-093
Swagelok 1/4" ferrule set   300-05375
Swagelok T-fitting 9881-181
Silicon septum 300-08998
Air pump; 12 VDC;
Maximum flow of 3.5 LPM		 The 12-volt diaphragm pump provides up to 3.5 LPM flow. 286-04198
Air pump; 6 VDC;
Maximum flow of 1.8 LPM		 The 6-volt diaphragm pump provides up to 1.8 LPM flow. 286-10198
Rotameter;
2.5 LPM with valve;
Requires two hosebarb fittings (part number 300-03388)		 Rotameter 294-03334

Other Suppliers

Contact LI-COR if you have questions regarding your instrument or about how to assemble an air flow system.