Reducing High Frequency Noise from the 7200-101 Flow Module

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In some situations, the 7200-101 Flow Module may emit high frequency noise through its exhaust port. This may occur if the motor drive of the Flow Module is ramped up to maintain the flow rate as pressure drops in the flow path. Inline filters that clog up over time may cause a significant motor drive increase, especially if the inline filter is not replaced before the motor drive reaches its maximum at 100%.


The silencer shown below in Figure 1‑1 can significantly reduce this high frequency noise.

Required parts:

(A) 1x 300-11179 HOSE BARB, 3/8”, NPT

(B) 2x 300-10788 HOSE CLAMP, 1/2” OD

(C) 1x 301-10381 AIR FILTER HOLDER

(D) ~15 cm 222-10384 Black Tygon tubing, 3/4” O.D.

You can cut off a short piece of the black Tygon tubing that connects the LI-7200 head to the Flow Module ‘AIR IN’ port.

Silencer Performance

As shown in , the silencer is reducing the (1) overall sound pressure as well as the (2) peak frequency, i.e., the high frequency noise. In this test, the overall noise was reduced by up to 14 dB. The more significant effect is the reduction of the peak noise frequency from a range of 2700 to 8000 Hz down to 30 to 440 Hz.

Figure 1‑1. Test of silencer effect on a 7200-101 Flow Module’s (FM1-0518) sound pressure [dB] and peak frequency [Hz] levels, depending on the Flow Module’s motor drive. The LI- 7200’s inlet geometry consisted of (1) rain cap v3, (2) clean 2 micron Swagelok inline filter, and (3) heated intake tube

See a video of the procedure at