KDG / KDF-2 - Micro Flow Meter and Switch

The KOBOLD KDG/KDF-2 is a micro rotameter, a variable area flow meter and switch designed to measure and monitor very low flows of liquids and gases. KDF versions serve liquids across nine standard ranges from 0.25-2.5 l/h to 16-160 l/h; KDG versions serve gases across fifteen standard ranges from 0.5-5 Nl/h to 500-5000 Nl/h. An integral precision needle valve is fitted as standard, so flow can be set precisely within the measuring range. Wetted parts are stainless steel, borosilicate glass, and FPM seals (FFKM optional), rated to 232 PSIG (PN 16) and 212°F (100°C). Every range can be fitted with one or two adjustable inductive proximity switches that signal set flow values, and an optional panel mounting kit is offered.

How the KDG/KDF-2 Micro Rotameter Works

The KDG/KDF-2 operates on the suspended float principle. The meter is installed vertically with flow from bottom to top, and a stainless steel ball float rises inside a borosilicate glass measuring cone. The reading point is the upper edge of the ball on easy-to-read, direct reading scales for water and air.

The instrument is designed as a compact, simple, and economical measuring system. Measure only clean, low viscosity, homogeneous liquids compatible with the materials of construction; dirt particles may block the float. When conditions deviate from the calibration data (flow range, medium, pressure, density, and temperature), readings can be adapted per VDI/VDE guideline 3513.

Flow Ranges, Accuracy, and Key Specifications

Water ranges run from 0.066-0.66 GPH (0.25-2.5 l/h) up to 4.2-42.3 GPH (16-160 l/h). Air ranges run from 0.5-5 Nl/h to 500-5000 Nl/h, referenced to 17.4 psia (1.2 bar absolute) and 68°F (20°C). Other liquids and gases are available on request.

• Accuracy: ±2.5% (qG = 50%, per VDE/VDI 3513); repeatability: ±1.0% of full scale
• Maximum pressure: 232 PSIG (PN 16)
• Process and ambient temperature: -4 to 212°F (-20 to +100°C); limited to 158°F (+70°C) with contacts
• Protection type: IP65 (EN 60529)
• Pressure drop: 0.15 to 2.9 psi (10 to 200 mbar), depending on model

Materials and Process Connections

All metal wetted parts are stainless steel: the fitting is grade 1.4401, and the float and valve stem are grade 1.4404. The measuring tube is borosilicate glass, the float stop is PTFE, the valve seat is PTFE with 25% carbon fibre, and gaskets are FPM as standard with FFKM as an option.

Process connections are ¼" NPT female or G ¼ female (rear-facing), or a polyamide hose nozzle for 0.31 in (8 mm) hose in straight or 90 degree angled form. Special connections can be requested.

Flow Switch Options: Monostable and Bistable

Two ring-type inductive switch types are offered. A monostable contact activates momentarily as the stainless steel float passes on rising or falling flow and is preferred as a minimum or maximum contact. A bistable contact activates as the float rises and stays active until the float falls back past it, so it works at any position on the measuring tube.

Connection is by junction box or by 6.6 ft (2 m) cable, with electrical characteristic values to DIN 19234 (NAMUR). An external isolation switching amplifier, offered as the KFD2-KFA5 accessory, is necessary for operation. Two contacts on one meter must be spaced at least 0.63 in (16 mm) apart. On models KDF-2239 through KDF-2241 and KDG-2257 through KDG-2268, the limit switch is available as a minimum contact only and can be used to approximately 50% of the maximum measuring range. Versions with ATEX approval for hazardous areas can be requested.

Optional Differential Pressure Controllers

Differential pressure controllers are designed to maintain a constant flow rate of liquids and gases in pipelines. Upstream pressure controllers (option codes E and F) hold flow constant with variable upstream pressure and constant downstream pressure; downstream pressure controllers (option codes A and B) handle variable downstream pressure and are the preferred choice for liquids.

The controller is stainless steel with an integrated FPM or PTFE membrane. It requires a minimum pressure difference of 5.1 psi (350 mbar) between inlet and outlet, and the maximum one-sided membrane load is 101.5 psi (7 bar).

Installation, Commissioning, and Maintenance

The KDG/KDF-2 is installed vertically, with the direction of flow from bottom to top. Clean the pipeline by blowing out or rinsing before connecting the device; piping should be attached centric and as stress-free as possible, and supported where necessary. An optional kit allows front mounting in a panel cut-out.

For commissioning, close the needle valve, open the shutoff valves upstream and downstream, vent the pipeline carefully for liquids, and let pressure rise slowly for gases to avoid glass breakage. Then open the needle valve and set the desired flow rate within the specified pressure and temperature maximums. The measuring glass can be replaced once the device is pressure free; offered spares include gasket sets, the protective cover, and limit switches.

Common Questions about KDG / KDF-2 - Micro Flow Meter and Switch