MODERNIZED PNEUMATIC FAN FOR VENTILATING BLIND MINE WORKINGS

B. M. Titov

In our article “A New Type of Pneumatic Fan” (see the journal Ugol’, No. 6, p. 33, 1951), a description was given and the characteristics were presented of the VP–4 unit¹, which since 1950 has been in series production at the Tomsk Electromechanical Plant named after V. V. Vakhrushev (TEMZ).

Fig. 1. General view of the VP-4M fan.

Two years’ operation of these fans under mine conditions has shown that the VP–4 unit is reliable in operation and successfully ventilates blind workings up to 200–250 m long.

Continuing work on improving the pneumatic fan, the team of designers at TEMZ, in collaboration with research staff of the Department of Mining Mechanics of the Tomsk Polytechnic Institute (TPI), has created a new modernized fan of the VP–4M type² (Figs. 1, 2).

The VP-4M unit consists of a fan with guide and straightening apparatuses and a pneumatic turbine. Compressed air is supplied through a three-channel nozzle to the air turbine and, after doing work in it, is discharged into the pipeline downstream of the fan; that is, when the unit operates in delivery mode it is used for ventilating the heading.

Fig. 2. Section of the VP-4M fan.

1—guide apparatus; 2—fan impeller; 3—straightening apparatus; 4—turbine; 5—nozzle; 6—channel for discharging the air that has done work in the engine; 7—valve for shutting off one nozzle channel.

When ventilating blind workings, it is not immediately necessary for the fan to create maximum pressure; therefore, in the VP-4M unit, power regulation is provided by shutting off one nozzle channel, i.e., a regulated partial supply of air to the turbine-engine impeller is effected.

Regulating power by this method is more economical than regulation by partial closing of the inlet valve, since it occurs without loss of compressed-air energy.

In short workings the fan is normally operated with two nozzle channels working; in this case, temporary switching-on of the third channel may be used for accelerated ventilation of the heading after blasting.

The main difference between the VP-4M unit and the VP-4 is as follows:

a) the nozzle design has been changed, and provision has been made for regulating the unit power by reducing the consumption of compressed air;

b) the design arrangement of the air-turbine exhaust has been changed;

c) the design of the flow-through part of the fan has been changed.

The characteristics obtained by the author of the article during testing of a perfected prototype of the VP-4M fan are shown in Figs. 3 and 4.

For comparison of the modernized unit with the series-produced one, Fig. 3 additionally shows the characteristic of the VP-4 fan and co-

compiling Table 1, from which it is evident that, for the modernized fan, with the best aerodynamic characteristic:

a) the total air consumption is lower by . . . . . . . . . . . . . . . . . . . . . . 7.5%
b) the specific air consumption at the turbo-drive shaft is lower by . . . . 26%
c) the fan efficiency is higher by . . . . . . . . . . . . . . . . . . . . . . . . . . 6%
d) the adiabatic efficiency of the unit is higher by . . . . . . . . . . . . . . 32%
e) regulation of the unit power is provided.

Fig. 3. Characteristics of fans of type VP-4 and VP-4M, at \(P_{\mathrm{in}} = 4.0\) atm:

1 — VP-4M with three nozzle channels switched on, \(Q_{\mathrm{dv}} = 4.25\ \mathrm{m^3/min}\); 2 — VP-4M, with two nozzle channels switched on, \(Q_{\mathrm{dv}} = 2.85\ \mathrm{m^3/min}\); 3 — VP-4, with \(Q_{\mathrm{dv}} = 4.65\ \mathrm{m^3/min}\).

Fig. 4. Characteristic of the VP-4M fan:

1 — at \(P_{\mathrm{in}} = 5.0\) atm and with three nozzle channels switched on, \(Q_{\mathrm{dv}} = 5.12\ \mathrm{m^3/min}\); 2 — at \(P_{\mathrm{in}} = 5\) atm and with two nozzle channels switched on, \(Q_{\mathrm{dv}} = 3.45\ \mathrm{m^3/min}\); 3 — at \(P_{\mathrm{in}} = 3.0\) atm and with three nozzle channels switched on, \(Q_{\mathrm{dv}} = 3.18\ \mathrm{m^3/min}\); 4 — at \(P_{\mathrm{in}} = 3.0\) atm and with two nozzle channels switched on, \(Q_{\mathrm{dv}} = 2.35\ \mathrm{m^3/min}\).

The characteristics of the fans shown in Figs. 3 and 4 correspond to their operation in discharge. When the unit operates in suction, however, its characteristic deteriorates somewhat, namely:

a) the static pressure of the fan decreases by 8–10 mm water column,

if a metal branch pipe 400 mm in diameter and 0.5–1.0 m long is not installed downstream of the fan;

Table 1

Note. The amount of air delivered to the working face was determined graphically by means of pipeline characteristics constructed with allowance for air leakage according to data from Giproglemash.

b) the output of the unit is reduced by the amount of air consumed by the turbomotor.

The air consumption by the motor and the maximum revolutions of the unit shaft as a function of changes in operating pressure in the pneumatic network are shown in Figs. 5, 6.

The air consumption by the turbomotor depends only on the minimum flow sections of the nozzle channels and does not depend on the revolutions of the unit shaft, since the nozzle operates at a pressure above the critical value.

The maximum revolutions of the unit shaft, as is evident from Figs. 3 and 4, are obtained when the fan operates without a pipeline. To reduce the centrifugal forces acting on the rim of the impeller, the blades of the VP-4M turbomotor are made of aluminum alloy.

To check mechanical strength, all impellers are tested for “overspeed” at 5700 rpm; therefore, operation of the VP-4M unit at impeller speeds above 5000 rpm is inadmissible.

The VP-4M was not tested under production conditions, since the general design configuration of the unit remained the same as that of the VP-4 fan, which has proved itself well in mine conditions.

The Department of Mining Mechanics of TPI and the team of designers of TEMZ intend in the future to develop the design of a sectional pneumatic unit with power regulation.

A sectional unit will make it possible to obtain such a fan characteristic as is necessary for ventilating a working of a given length and thereby to reduce significantly the consumption of compressed air. Each section of the unit must constitute an independent fan designed for ventilating a working 75–100 m long, and for ventila-

...of longer workings, provision should be made for connecting them in series into a block without intermediate branch pipes.

Taking into account that different quantities of air must be supplied to workings of different cross-section and length, it is expedient to manufacture the fan sections with diameters of 0.3, 0.4, and 0.5 m.

On the basis of operating experience and investigation of the working process of the VP-4 and VP-4M fans, the following conclusions may be drawn:

1. The structural design of the VP-4M unit is fully suitable for its operation under mine conditions.

Fig. 5. Air delivery by the VP-4M turbo-fan as a function of the change in working pressure in the network:

1 — with three nozzle channels switched on;
2 — with two nozzle channels switched on.

Fig. 6. Dependence of the shaft speed of the VP-4M unit on the change in working pressure in the network when the fan operates without a duct:

1 — with three nozzle channels switched on;
2 — with two nozzle channels switched on.

1. The VP-4M fan is 32% more economical than the VP-4 fan, even without taking into account the possibility of regulating the power of the unit by switching off one nozzle channel.

2. At a working pressure in the network of 5 atm, the VP-4M fan can be used for ventilating blind workings up to 300–350 m long.

3. When the VP-4 and VP-4M fans operate on suction, it is advisable to install, behind the fan, a metal branch pipe 400 mm in diameter and 0.5–1.0 m long.

4. For ventilating blind workings, in order to save expensive pneumatic energy, it is advisable to use sectional fans with power regulation.

The latter provision can also be successfully extended to electric fans for auxiliary ventilation.

1. Pneumatic fan for pipelines 400 mm in diameter. ↩

2. The same—modernized. ↩