Here are some principles and basic conditions for selecting hydraulic gear pumps

Here are some principles and basic conditions for selecting hydraulic gear pumps

According to the principles and basic conditions for selecting hydraulic gear pumps, the specific operation is as follows:
1. Based on the nature of the liquid medium, determine whether to choose a clear water gear pump, hot water gear pump, oil gear pump, chemical gear pump, corrosion-resistant gear pump, impurity gear pump, or a non-clogging gear pump. For gear pumps installed in explosion-proof areas, explosion-proof motors of the corresponding grade should be used according to the explosion-proof area classification.
2. Based on the layout of the equipment, terrain conditions, water level conditions, and operating conditions, determine whether to choose horizontal, vertical, or other types (pipe type, submersible type, submerged type, non-clogging type, self-priming type, gear type, etc.) of gear pumps.
3. Determine the specific model of the gear pump. After determining the series of the gear pump to be selected, the main parameters of the maximum flow rate (if there is no maximum flow rate, usually take 1.1 times the normal flow rate as the maximum flow rate) and the head with a 5% to 10% margin can be used to determine the specific model on the type spectrum diagram or series characteristic curve. The operation is as follows:
Use the characteristic curve of the gear pump, find the required flow rate value on the horizontal axis, and find the required head value on the vertical axis. Draw vertical and horizontal lines from the two values respectively. If the intersection point of the two lines falls exactly on the characteristic curve, then this gear pump is the one to be selected. However, this ideal situation is rare. Usually, the following two situations will occur:
The first situation: The intersection point is above the characteristic curve, which indicates that the flow rate meets the requirements, but the head is insufficient. In this case, if the head difference is not significant or is about 5%, the gear pump can still be selected. If the head difference is large, a gear pump with a larger head should be selected or the pipeline resistance loss should be reduced.

The second type: If the intersection point is below the characteristic curve and within the fan-shaped trapezoidal range of the gear pump's characteristic curve, then this model is initially determined. Then, based on the difference in head, it is decided whether to cut the diameter of the impeller.

If the head difference is very small, no cutting is required. If the head difference is very large, the impeller diameter should be cut according to the required Q and H, based on the cutting formula. If the intersection point does not fall within the fan-shaped trapezoidal range, the gear pump with the smaller head should be selected. When choosing a gear pump, sometimes the production process requirements must be considered, and gear pumps with different Q-H characteristic curves should be selected. 4. According to the flow rate, determine whether to choose a single-suction gear pump or a double-suction gear pump; according to the head, choose a single-stage gear pump or a multi-stage gear pump, a high-speed gear pump or a low-speed gear pump (air conditioning gear pump). The efficiency of a multi-stage gear pump is lower than that of a single-stage gear pump. If both a single-stage gear pump and a multi-stage gear pump can be used, the single-stage gear pump should be selected first.

After the gear pump model is determined, for water gear pumps or gear pumps that convey media with physical and chemical properties similar to water, it is necessary to refer to the relevant product catalog or sample again. Based on the performance table or performance curve of this model, check whether the normal operating point falls within the preferred operating zone of the gear pump.

6. For gear pumps transporting liquids with a viscosity greater than 20 mm²/s (or a density greater than 1000 kg/m³), it is essential to convert the characteristic curve of the gear pump tested with water into the performance curve under the given viscosity (or density). Special attention should be paid to the careful calculation or verification of suction performance and input power.

7. Determine the number of gear pumps and the standby rate: For normal operation, only one gear pump is usually used because a large gear pump is equivalent to two small gear pumps working in parallel (referring to the same head and flow rate). The efficiency of a large gear pump is higher than that of a small gear pump. Therefore, from an energy-saving perspective, it is better to choose one large gear pump rather than two small ones. However, in the following circumstances, two gear pumps working in parallel can be considered:

The flow rate is very high, and one gear pump cannot achieve this flow rate.

For large gear pumps that require a 50% standby rate, two smaller gear pumps can be operated while one is kept as a standby (a total of three).

For some large gear pumps, it is possible to operate two gear pumps in parallel with a capacity of 70% of the required flow rate, without the need for a spare gear pump. When one gear pump is under maintenance, the other can still handle 70% of the production's conveying requirements.

For gear pumps that need to operate continuously for 24 hours without interruption, three gear pumps should be prepared: one in operation, one on standby, and one under maintenance.

Under normal circumstances, customers can submit their "basic conditions for selecting gear pumps", and the pump manufacturing enterprise will provide selection or recommend better gear pump products. If the design institute has already determined the model of the gear pump when designing the equipment, it will be configured according to the requirements of the design institute.

When selecting a gear pump, it is necessary to comprehensively consider factors such as working pressure, flow rate, rotational speed, fixed or variable displacement, variable displacement mode, volumetric efficiency, overall efficiency, service life, type of prime mover, noise, pressure pulsation rate, self-priming ability, etc. Additionally, compatibility with hydraulic oil, size, weight, economy, and maintainability should also be taken into account. Some of these factors are already listed in product samples or technical documents, which should be carefully studied. For unclear points, it is best to consult the relevant gear pump selection manual of a legitimate gear pump manufacturer.

The above:The working principle of flow control valve and pressure control valve