Network pumps are designed to supply hot water through heating networks. The main parameters of the pumps were regulated by GOST 22465-77.
Depending on the installation location, they are used as pumps:
– the first rise, supplying water from the return pipeline to the heaters;
– second rise to supply water after the heaters to the district heating network;
– recirculation installed after hot water boilers.
Basic requirements for the design of network pumps:
– work under conditions of significant fluctuations in temperature and pressure;
– stable, continuously decreasing shape of the pressure characteristic in the flow range of 20-110% of the nominal, ensuring reliable parallel operation.
Network pumps must operate reliably over a wide flow range. Changing the parameters of individual types of pumps can be achieved by trimming the impellers along the outer diameter within the limits specified by the manufacturer. The reduction in efficiency should not exceed 3%.
Since the temperature of the pumped water varies within 120-180 °C, the design of network pumps, unlike general-purpose pumps, ensures free thermal expansion of the pump elements, and the rotor end seals have a cooling system (thermal barrier), like other “hot” pumps.
Depending on the pressure created, network pumps can be one- and two-stage spiral type with a horizontal connector, with double-entry impellers (type D), with synchronous rotation speeds of 1500 and 3000 rpm.
Depending on the size, they can be supplied on either a common or separate foundation slab.
The materials of the main parts of network pumps are gray cast iron and chromium steel.
As examples of design, let’s consider network pumps SE 500-70-16 and SE-1250-140-11.
- Network pump SE 500-70-16 (Figure 1) – centrifugal, single-stage, horizontal, spiral type, with a double-entry impeller.
The basic part of the pump is a housing with a horizontal split in a plane passing through the axis of the pump. The pump casing is a cast iron casting of complex shape, consisting of two parts (pump cover and pump body), in which semi-spiral inlet and double-spiral outlet channels are cast, as well as chambers (thermal barriers) for supplying and discharging coolant to the end seals. Inlet and discharge pipes, support legs and trough-shaped brackets for collecting leaks, as well as mounting the bearing housing, are also cast in the lower part of the housing. The location of the inlet and discharge pipes in the lower part of the housing makes it possible to disassemble the pump without dismantling the pipelines. The pipes are directed horizontally in opposite directions. The horizontal connector is sealed with a paronite gasket. The studs on the connector are tightened with cap nuts to prevent hot water from seeping through the threads of the studs. The housing with four legs, the supporting surfaces of which are as close as possible to the axis of the pump to reduce misalignment when the pump heats up, rests on the pedestals of the foundation frame. To ensure directed thermal expansion of the pump, pins are installed in the lower part of the housing, acting as guide keys. In the upper part of the pump housing (cover) there is a plugged hole for air release. In places where the impeller is sealed in the pump housing, sealing rings are installed.
The pump rotor is an independent unit and consists of a shaft, impeller, oil seal bushings, left bushing, right bushing and fasteners. The impeller consists of two halves and is mounted on the shaft using a sliding fit. Torque is transmitted to the impeller using a key. From axial movements, the impeller is fixed on the shaft by left and right bushings. The oil seal bushings are secured against axial movement with set screws. To compensate for thermal expansion of the rotor parts, thermal gaps are provided between them. The rotor is statically balanced after assembly.
The rotor is relieved from axial forces by using a double-entry impeller.
The shaft seal is stuffing box type. In order to ensure the temperature regime in the stuffing box, coolant is supplied and discharged to the thermal barriers. To unload the seal, an annular throttling slot is made in front of it. Leaks through the stuffing box are collected in a trough and discharged to the drain.
It is possible to install mechanical seals.
The pump rotor is supported by rolling bearings, which are installed in split housings. The support bearing on the drive side absorbs radial loads. The thrust bearing on the side of the free end of the shaft absorbs residual axial forces and radial loads. Bearings are lubricated with liquid, ring (crankcase) lubrication using a spray disc. Oil level indicators are provided to monitor the oil level. The bearing housings are equipped with chambers for water cooling.
Aligning the rotor with the stator carried out by moving the bearing housings with adjusting screws. After final alignment, the bearing housings are fixed relative to the pump housing with tapered pins.
Within the pump there is a system of auxiliary piping for cooling the rotor end seals and bearing units.
An asynchronous motor with a squirrel-cage rotor is used as a drive.
The pump and motor are connected to each other using an elastic pin-sleeve coupling. The coupling is closed by a guard.
The symbol of the pump means: SE – network electric pump; 500 – flow rate in m3/h; 70 – head in m; 16 – inlet pressure in kgf/cm2.
Figure 1
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- Network pump SE 1250-140-11 (Figure 2) – centrifugal, two-stage, horizontal, spiral type, with double-entry impellers.
The basic part of the pump is a housing with a horizontal split in a plane passing through the axis of the pump. The pump casing is a cast iron casting of complex shape, consisting of two parts (pump cover and pump body), in which the channels of semi-spiral inlets and spiral outlets are cast. Inlet and discharge pipes, support legs and trough-shaped brackets for collecting leaks, as well as mounting the bearing housing, are also cast in the lower part of the housing. The location of the inlet and discharge pipes in the lower part of the housing makes it possible to disassemble the pump without dismantling the pipelines. The pipes are directed horizontally in opposite directions. The horizontal connector is sealed with a paronite gasket. The studs on the connector are tightened with cap nuts to prevent hot water from seeping through the threads of the studs. To supply water from the first to the second stage of the pump, a transfer pipe is provided in the upper part of the housing (lid). To reduce leaks, a diaphragm is installed between the stages. There are holes for air release in the upper part of the transfer pipe and the pump housing (cover), and holes for draining water from the pump in the lower part of the pump housing. When the pump is running, the holes are closed with plugs. To reduce possible vertical temperature movements of the housing, the supporting surfaces of the feet are as close as possible to the axis of the pump and with them the pump rests on the pedestals of the foundation frame. To ensure directed thermal expansion of the pump, pins are installed in the lower part of the housing, acting as guide keys. In places where the impellers are sealed in the pump housing, sealing rings are installed.
The pump rotor is an independent unit and consists of a shaft, impellers, protective sleeves, bushings, bearing sleeves, oil deflectors and fasteners. Double-entry impellers, mounted on the shaft using a sliding fit, rest against protective bushings and are fixed axially through the oil seal bushings with round nuts. To compensate for thermal expansion of the rotor parts, thermal gaps are provided between them. The rotor is dynamically balanced after assembly. The rotor is relieved from axial forces by using double-entry impellers.
The shaft seal is an stuffing box type with cooling. In order to ensure reliable operation of the gland seal, gland bushings are installed in the pump housing, forming chambers (thermal barrier) into which coolant is supplied. The coolant supplied to the oil seal is divided into two streams. One flow washes the outside of the stuffing box and is discharged into the drain pipeline, the other flow through the hole in the stuffing box enters the lantern ring and is supplied to the packing. Leaks through the stuffing box are collected in a trough and discharged into the leakage pipeline. The design provides for unloading of the second stage gland by draining water from the gland through the unloading pipe into the first stage inlet. Leaks through the stuffing box are collected in a trough and discharged to the drain.
It is possible to install mechanical seals.
The pump rotor is supported by rolling bearings, which are installed in split housings. The bearing housings are made of two halves with a horizontal split. A roller bearing is installed in the support bearing housing on the drive side, which absorbs radial loads. In the thrust bearing housing, on the side of the free end of the shaft, two angular contact ball bearings are installed, which absorb residual axial forces and radial loads. Bearings are lubricated with liquid, ring (crankcase) lubrication using lubricating rings. Oil level indicators are provided to monitor the oil level. There are chambers in the bearing housings, and also refrigerators are installed into which coolant is supplied to cool the oil.
Alignment of the rotor with the stator is carried out by moving the bearing housings with adjusting screws. After final alignment, the bearing housings are fixed relative to the pump housing with tapered pins.
Within the pump there is a system of auxiliary piping for cooling the rotor end seals and bearing units.
An asynchronous motor with a squirrel-cage rotor is used as a drive.
The pump and motor are connected to each other using an elastic pin-sleeve coupling. The coupling is closed by a guard.
The symbol of the pump means: SE – network electric pump; 1250 – flow in m3/h; 140 – head in m; 11 – inlet pressure in kgf/cm2.
Figure 2
