Brooks Instrument MT3750C Metal Tube Variable Area Flow Meter

A compact metal-tube meter for low flows in harsh service

The MT3750C is a Brooks Instrument metal tube variable area flowmeter for low flow rates of gas and liquid in harsh environments. The tube and end fittings are 316L stainless steel or Monel K-500, which the datasheet presents as a compact, cost-effective replacement for glass tube flowmeters where pressure, temperature or hazardous-area rules make glass unsuitable. Water ranges reach up to 100 l/h (26 gph).

The meter is offered with threaded connections only, in a compact body that fits into tight spaces. Optional cartridge or NRS needle valves, integrally mounted flow controllers, inductive or reed-switch alarms and a 4-20 mA transmitter add control and signalling. The datasheet gives ATEX, CSA and IECEx approvals for the explosion-proof and intrinsically safe versions, so the exact option must be matched to the zone.

Technical specifications

Using the sizing tables and model code

Table 2 of the datasheet lists the flow range, viscosity limit and pressure drop of each meter size from A and 0 to 6 on water and air. Viscosity immunity ceilings run from 5 cP on the smallest sizes to 130 cP on size 6, with a calculated correction when the process fluid is more viscous than the calibration fluid. Capacities are based on a 316L float for sizes 1 to 6 and a titanium float for size 0.

The model code adds connection type and size, horizontal connection orientation, the valve configuration (no valve, low, medium or high flow valve, NRS valve, or a mounted 8802, 8805, 8902 or 8905 flow controller) and accuracy and scale options for liquid, gas or high-viscosity liquid. Electrical output, power supply and the certification letter follow.

What to confirm before ordering

Send the fluid, density or molecular weight, viscosity, the flow range in the units you want on the scale, operating pressure and temperature, ambient temperature, connection, valve preference, alarm or transmitter need and the zone classification. The datasheet warns that gas pressure should be raised gradually to avoid the float hitting the float stop. The Brooks MT3750C name replaces plain MT3750 in the datasheet title, so quote the full model code from your nameplate when asking for a quotation.

Key features

• All-metal 316L stainless steel or Monel K-500 metering tube, suitable where glass tube meters are not acceptable.
• Very low flow ranges, from 0.096 l/h of water on the smallest size.
• Pressure ratings up to 100 bar, or 276 bar for the high-pressure 1/4 inch NPT version without valve.
• Local indication with no power required; alarms and a 4-20 mA transmitter are optional.
• Integral needle valves or 8800/8900 series flow controllers for a complete purge or dosing set in one compact unit.
• IP66/67 and NEMA 4X die-cast aluminium housing with ATEX, IECEx and CSA approved versions.

Typical applications

• Instrument and analyser purge flows with nitrogen or air.
• Chemical injection and additive dosing at low rates in oil and gas facilities.
• Sample conditioning systems for process analysers.
• Seal flush and bearing cooling flows on pumps.
• Low-flow gas blanketing of tanks and vessels.

Selection guidance

Choose the meter size so that the normal flow falls in the upper part of the scale, which improves readability and makes better use of the stated accuracy, as accuracy is given as a percentage of full scale. Match the O-ring material to both the fluid and the temperature: Kalrez 4079 and PTFE cover the widest range, while Buna and ethylene propylene are limited to 120 °C. Use a flow controller instead of a simple needle valve where the upstream or downstream pressure varies and a constant flow is required.

Installation and use in Oman and GCC facilities

Variable area meters must be installed vertically with flow upwards, free of stress from the piping. Clean the line before installation, because particles can jam a small float. In the region, many of these meters are fitted on outdoor analyser shelters and wellhead or injection skids, where sun can heat the housing well above air temperature. The maximum fluid temperature is reduced as the ambient temperature rises, so check the datasheet tables for summer conditions, and shade the meter where possible. For hazardous areas in oil and gas plants, confirm the zone, gas group and temperature class against the certification on the model code, and use suitable cable glands to maintain the IP rating against dust.

Documents and quotation

The manufacturer datasheet (16 pages) is attached to this page as a download. For a quotation, send the full model code and the process data to Seven Star LLC in Muscat; browse more instruments in the Flowmeters category. We supply this item as an independent supplier, so please confirm availability and delivery with us.