Most plant pressure gauges read in bar or psi, and a 0-10 bar dial cannot show the few millibar that matter on a boiler draft, a burner fuel-gas train, a ventilation duct or a filter housing. Those duties are measured in inches or millimetres of water, and a standard Bourdon-tube gauge at that scale barely moves its pointer. A low-pressure diaphragm gauge is built for exactly this range.
This note looks at the Miljoco LP2507L, a 2½" low-pressure diaphragm gauge for pressure and vacuum up to 10 psi, and its stainless steel U-clamp sister, the Miljoco LP2567. Figures come from the Miljoco low-pressure gauge datasheets hosted on our product pages and from the current Tetracon product pages. Where we give general engineering advice, it is labelled as general. No prices are given; range codes and connections should be confirmed at quotation.
Why low pressures need a diaphragm gauge
- The numbers are small. One inch of water column is about 2.49 mbar (249 Pa), so a full 0-10 inH2O scale is only about 25 mbar, and 10 psi is about 689 mbar (general conversions). On a gauge ranged in bar these pressures are lost in the first scale division.
- A diaphragm gives a usable scale. The LP2507L uses a single beryllium-copper diaphragm fixed to a precision-machined brass plate, with a brass movement with precision-milled teeth and a nickel-silver pinion and bearing surface (datasheet). A diaphragm has a large area, so a few millibar produce a full pointer sweep.
- Typical duties. The datasheet lists gas-draft indication, air flow and filtration, and leak detection, for pressure and vacuum applications up to and including 10 psi. The LP2567 datasheet adds medical pumps.
How the LP2507L is built
The LP2507L has a 2½" aluminium dial (white with black markings), a black non-adjustable pointer, a black drawn steel case and a quarter-turn polycarbonate lens. The brass socket has a 1/4" NPT bottom connection; the LP2507 is the same gauge with a 1/4" NPT back connection for panel or wall mounting. Ranges above 10" H2O are fitted with a 0.013" restrictor (datasheet), which helps steady the pointer against pulsation (general).
The LP2567 uses the same diaphragm, movement and standard ranges in a brightly finished 300 series stainless steel case with a threaded polycarbonate lens, a U-clamp for panel mounting and a 1/4" NPT back connection (datasheet). All three are dry gauges with no liquid fill.
Miljoco LP2507L at a glance
| Item | LP2507L / LP2507 datasheet |
|---|---|
| Type | 2½" low-pressure diaphragm gauge, pressure and vacuum up to and including 10 psi, dry |
| Accuracy | ±1.5 % of full scale (exceeds ASME B40.100 Grade B); ranges below 30" H2O are 3-1-3 % |
| Element | Single beryllium-copper diaphragm on a precision-machined brass plate |
| Movement | Brass, precision-milled teeth; nickel-silver pinion and bearing surface |
| Pressure ranges (inH2O) | 0-10, 0-15, 0-30, 0-60, 0-100, 0-160, 0-200; dual 0-35" H2O / 0-20 oz/in²; many ranges also in oz/in² |
| Vacuum ranges (inH2O) | 15-0, 30-0, 60-0, 100-0, 160-0 vacuum |
| psi and compound | 0-3, 0-5, 0-10 psi; 30-0-30 compound |
| Restrictor | 0.013" on ranges over 10" H2O |
| Connection | 1/4" NPT brass socket: bottom (LP2507L) or back (LP2507) |
| Case / lens | Drawn steel, black / polycarbonate, quarter-turn |
| Dial / pointer | Aluminium, white with black markings / black, non-adjustable |
| Process temperature | -40 to +70 °C (-40 to 160 °F) |
| Ambient temperature | -40 to +60 °C (-40 to 140 °F) |
| Ordering | Model number plus range code, for example LP2507L 232 for 0-35" H2O / 0-20 oz/in²; other custom ranges on request |
The "3-1-3 %" notation follows ASME B40.100 practice: ±3 % of span in the first and last quarters of the scale and ±1 % in the middle half (general). For the best reading on these low ranges, choose a range that puts normal operation near the middle of the dial (general).
Where it fits
- Draft on boilers, furnaces and kilns. The datasheet names gas-draft indication. The standard vacuum ranges run from 15-0 to 160-0 inH2O, with a 30-0-30 compound range, which suits induced-draft fans, ducts and kilns with stronger suction (general). Natural and balanced-draft readings are often a fraction of an inch of water; for those, ask about a custom range or use the ACI DLP with its 0.1-1" WC span (general). Pair draft readings with flue-gas oxygen for combustion tuning (general).
- Low-pressure fuel gas. The product page lists low-pressure gas systems. Typical points are the burner side of a gas pressure regulator and the inlet to a gas train, where readings in inches of water are the norm (general). Check the burner manufacturer's required pressure and select a range that puts it mid-scale.
- Air flow and filtration. Listed in the datasheet. A single LP2507L reads the static pressure at one point, such as a fan outlet, a plenum or a dust collector housing, against atmosphere (general). For the pressure drop across a filter, use two tapping points or a true differential instrument such as the ACI DLP.
- Leak detection and tightness checks. Also listed in the datasheet. A low-range gauge on an isolated, pressurised section of low-pressure pipework or ductwork shows a falling pressure much earlier than a bar-range gauge would (general). Follow the test procedure and code that applies to the system.
- HVAC and clean air systems. The product page lists HVAC low-pressure monitoring. A local dial at an air handling unit is a simple, power-free check alongside the BMS (general).
Installation and selection notes
- Choose the range by normal operating pressure. Aim for normal operation in the middle half of the scale, where the 3-1-3 accuracy band is tightest on ranges below 30" H2O (general).
- Respect the overall limit. These gauges cover pressure and vacuum up to and including 10 psi (about 689 mbar). Never fit one where the line can see full supply pressure, for example upstream of a regulator; use an isolating valve and, if needed, overpressure protection (general).
- Mount for the reading you need. LP2507L for a bottom (stem) connection on a pipe or tapping; LP2507 for a back connection on a panel or wall; LP2567 when you want a stainless steel case and U-clamp panel mounting (datasheet).
- Check media compatibility. Wetted parts include the beryllium-copper diaphragm and brass socket. Copper alloys are not suited to ammonia and some corrosive or sour gases, so confirm the gas composition before ordering (general). For ammonia refrigeration, use Miljoco's dedicated PSF2598L / PSF4098L ammonia gauges instead.
- Keep temperature in range. Process temperature is -40 to +70 °C and ambient -40 to +60 °C (datasheet). On draft connections close to a hot flue, use a sufficient length of impulse line so the gauge stays within limits (general).
- Keep impulse lines clean and dry. At a few millibar, a little condensate in a sagging line changes the reading. Slope impulse lines so condensate drains away from the gauge, and add a drain point on flue-gas service (general).
Other low-pressure options from Tetracon's principals
| Duty | Product | From the datasheet / product page |
|---|---|---|
| Local dial reading, inH2O or oz/in², bottom connection | Miljoco LP2507L (LP2507: back connection) | 2½" diaphragm, ±1.5 % FS, pressure and vacuum up to 10 psi, drawn steel case |
| Same ranges, stainless case, panel U-clamp | Miljoco LP2567 | 2½" diaphragm, ±1.5 % FS, 300 series stainless steel case, 1/4" NPT back |
| Differential pressure with an electrical output (filters, ducts, rooms) | ACI DLP | Selectable 0.1-1", 1-10", 10-40" WC spans (uni/bidirectional), ±0.50 % FSO, 4-20 mA, 0-5 or 0-10 VDC, optional LCD |
| Air pressure testing of piping at psi levels | Miljoco P2008LATG | 2" air test gauge, 0-15 to 0-100 psi, 3-2-3 % (Grade B), bleed port |
| Higher process pressures | Miljoco P4509LX / Weiss NF4UGY / LF4UGY | 4½" gauges, ±0.5 % (Grade 2A); Weiss in brass, 316L SS or Monel, dry or liquid filled |
Use a dial gauge where a local, power-free reading is enough, and a transmitter such as the ACI DLP where the value must go to a BMS, PLC or alarm (general). Many sites use both: a transmitter for the control system and a local dial for operators and maintenance checks.
What to send with an enquiry
- The duty (draft, fuel gas, duct or filter housing, leak test or other) and the gas or air being measured.
- Normal operating pressure or vacuum and the maximum the gauge could ever see, with units.
- Preferred units on the dial: inches of water, oz/in² or psi.
- Mounting: bottom connection (LP2507L), back connection (LP2507) or stainless U-clamp panel mount (LP2567).
- Whether a local dial is enough or you also need an electrical output to a BMS or PLC.
FAQ
What is the Miljoco LP2507L?
A 2½" low-pressure diaphragm gauge from Miljoco Corporation for pressure and vacuum up to and including 10 psi. It uses a single beryllium-copper diaphragm and a brass movement, with a 1/4" NPT bottom connection and a black drawn steel case.
How accurate is it?
The datasheet gives ±1.5 % of full scale, which exceeds ASME B40.100 Grade B. Ranges below 30" H2O are 3-1-3 %.
What ranges are available?
Standard ranges run from 0-10 to 0-200 inches of water, vacuum from 15-0 to 160-0 inches of water, a dual 0-35" H2O / 0-20 oz/in² scale, 0-3, 0-5 and 0-10 psi, and a 30-0-30 compound range. Other custom ranges are available from the factory.
What is the difference between the LP2507L, LP2507 and LP2567?
The LP2507L has a bottom connection and the LP2507 a back connection, both in a black drawn steel case. The LP2567 has the same element and ranges in a 300 series stainless steel case with a U-clamp for panel mounting and a back connection.
Can it measure the pressure drop across a filter?
The LP2507L reads pressure at one point against atmosphere. For a true differential reading across a filter, use a differential instrument such as the ACI DLP transmitter, which has selectable spans from 0.1-1" to 10-40" WC.
What temperatures can it handle?
Process temperature -40 to +70 °C and ambient temperature -40 to +60 °C, according to the datasheet.
Next steps
Tetracon (Pvt.) Ltd. is the sole authorized agent for Miljoco Corporation in Pakistan and supplies Miljoco gauges and thermometers with local technical support. Send us your duty, operating pressure, dial units and mounting, and we will propose the right range code. Use the contact page or see our services. Start with the LP2507L, compare the LP2567, ACI DLP, P2008LATG and P4509LX, browse process instruments, or see all Miljoco products and the full product catalogue. Related notes: industrial pressure gauge selection, differential pressure monitoring for cleanrooms and HVAC and in-situ combustion O2 for boilers and furnaces. Free technical guides are collected under Guides.