Technical Specifications of ZLD-2 Coal Seam Borehole Flow Meter with Orifice Plate

ZLD-2 Orifice Plate Flowmeter Coal Seam Borehole Flowmeter Technical Specifications

The ZLD-2 Borehole Multi-stage Flowmeter is used to measure the initial velocity of gas emission from coal seam boreholes, in order to predict the risk of coal and gas outbursts in the coal body ahead of the working face and to verify the effectiveness of measures to prevent coal and gas outbursts. It can also be used to determine the effective influence radius of advanced outburst prevention boreholes.
Application Areas of the ZLD-2 Orifice Plate Multi-stage Flowmeter: Used underground for direct measurement in mining faces, cross-cut coal uncovering faces, and as supporting instrumentation for assessing regional outburst risks in coal seams.
Principle and Construction

ZLD-2 Orifice Plate Flowmeter Coal Seam Borehole Flowmeter is designed based on the nozzle throttling principle. When gas flows through the nozzle, the cross-section of the flow stream contracts, creating a pressure difference on both sides of the nozzle. The greater the flow rate, the larger the pressure difference. For a given pressure difference, a larger nozzle aperture allows a greater gas flow rate. The flowmeter is designed with five nozzles of different apertures; changing the nozzle allows for different flow measurement ranges. The instrument has a simple structure, as shown in the diagram. The main body is machined from a single piece of glass plate, consisting of a water column (1), nozzle (2), gas inlet (3), stopcocks (4, 5), and nozzle base (6). The instrument's dimensions are 250 x 120 x 34 mm, and it weighs approximately 0.8 kg.

ZLD-2 Orifice Plate Flowmeter Coal Seam Borehole Flowmeter Measurement Procedure
1. Preparation Before Measurement
Fill the water column gauge with water and adjust both sides to the zero mark; check the instrument's sealing performance. If the seal fails, replace the "O" ring seal; based on coal seam conditions, estimate the flow rate and select a nozzle with a closely matching flow range, then install it on the flowmeter nozzle base.
2. Method and Steps
This flowmeter is used in conjunction with the JN-1 type sealing device. During outburst risk prediction and effectiveness testing of outburst prevention measures at the working face, after drilling is completed, quickly insert the sealing device to seal the hole. Then connect the exhaust pipe of the sealing device to the flowmeter's gas inlet using a hose, ensuring the flowmeter's water column is in a vertical position. At this time, gas emitted from the coal body passes through the measurement chamber, exhaust pipe, connecting hose, and flowmeter nozzle, creating a pressure difference on both sides of the water column. Read the pressure difference value from the water column gauge.
The entire measurement process must be completed within 2 minutes.
Determination of Indicators for ZLD-2 Orifice Plate Multi-stage Flowmeter
The initial velocity of gas emission from the borehole, q (L/min), is calculated as follows:
Q = K · K1
Where: K — Flow coefficient of the selected nozzle, L/min·mm;
This coefficient is determined experimentally and provided in the instrument's manual upon delivery.
K1 — Gas concentration correction factor. Since methane concentration in coal seam gas is typically above 95%, this factor is taken as 1.34;
Δh — Pressure difference reading from the water column gauge, mm.
The critical value for the initial velocity of gas emission from the borehole should be determined based on actual measurements from the coal seam of each mine. In the absence of measured data, refer to the values listed in Table 1.
Table 1 Critical Values for Initial Gas Emission Velocity Indicators in Outburst Risk Prediction Boreholes
Volatile Matter of Coal 5–15 15–20 20–30 >30
qm 5.0 4.5 4.0 4.5
Table 2 Nozzle Series Table
Nozzle No. 1 2 3 4 5
Nozzle Aperture D (mm) 0.5 1.0 2.5 5.0 7.0
Nozzle Coefficient K (L/min·mm) 0.033 0.130 0.83 3.250 6.370
Flow Measurement Range (Methane) (L/min) 0.09–0.55 0.35–20.20 2.18–13.78 8.71–55.08 17.07–107.97
The design incorporates five nozzles with different apertures. Due to limitations in nozzle machining precision, the nozzle series for nozzles of the same diameter may vary. Therefore, each nozzle is calibrated on a calibration instrument before leaving the factory to obtain the actual nozzle coefficient. Table 2 provides the nozzle series for the five designed nozzles.
ZLD-2 Orifice Plate Multi-stage Flowmeter Technical Parameters
Range: 0–1.6 kPa
Flow Measurement Range: 0–100 L/min
Instrument Weight: 0.8 kg
Flow Measurement Range 0.1–100 L/min
Water Column Pressure Difference Reading 0–160 mm
Instrument Resolution 1 mmH₂O
Precautions for ZLD-2 Orifice Plate Multi-stage Flowmeter Measurement
Ensure effective sealing of the instrument's "O" ring seals. Nozzles should be kept clean, with no debris blocking the throttling orifice, to maintain smooth gas flow.
During measurement, rotate the two-way stopcock (3) counterclockwise until it is fully in place, ensuring effective sealing of the internal 8 x 1.9 specification "O" ring seal.

Zhengzhou Aidi produces ZLD-2 Orifice Plate Flowmeter Coal Seam Borehole Flowmeter, supplies coal drill cuttings desorption instruments, deep hole sampling devices, pressure measurement instruments, geological exploration desorption instruments, borehole flowmeters, mine gas drainage and outburst prevention equipment, true density measuring instruments for coal, gas content measuring instruments, automatic initial gas emission velocity measuring instruments, diffusion velocity measuring instruments, coal gas drainage pipeline gas parameter instruments, and borehole coal powder circulation devices.