Direct Pump Guide

Direct Pumps, also known as direct-drive pumps, are a type of hydraulic pumps that are powered by electric motors. Designers and engineers have come up with different types of structures for different applications. Some situations demand the use of a direct drive structure of motor and pump, while for others an indirect solution is more suitable. In this article, we will focus on the structure, advantages, and disadvantages of a direct drive pump. The final section will also take a look at direct pumps and water garden applications.

The Basics

The direct-drive pump is composed of a shaft connecting the motor and the pump. They are cheap, simple, and eliminate all lateral loads on the pump bearings. But direct drives are still only suitable for a small number of applications. This is because the direct-drive pump and motor must be installed firmly and accurately to ensure that the pump and motor shafts are aligned. The pump may require the pilot surface to mate with the pilot hole on the mounting pad. Even with guide surfaces, technicians must be very careful during installation. For certain applications, a similar set of pumping elements may be placed on an extended motor shaft to ensure proper alignment. The completed configuration is practically identical to the integrated pump motor setup.

Direct Coupling Drive Pumps

There are also direct coupling drive pumps, which means that a flexible coupling connects the shaft and the pump. This is one of the most common methods when it comes to driving a pump. It has most of the advantages of direct drive but does not require precise shaft alignment. The lateral load of the bearing is usually low, but it is proportional to the misalignment of some coupling types, and the drive is simple. The couplings commonly used in this type of drive should accommodate the angle of the intersecting axis and the offset or disjoint axis.

The Pros and Cons

The flange of the direct-drive pump is installed on the end face of the engine or the shaft end of the motor. The speed of a common gasoline engine is about 3450 RPM. Since the pump is directly connected to the engine shaft, the RPM of the pump is the same as the RPM of the engine. Electric motors usually drive direct-drive pumps at 3450 RPM or 1725 RPM. The direct-drive pump allows the design of a more compact high-pressure cleaner.

Another advantage is that the drive system is simple and has few moving parts; therefore it is cheaper. The disadvantage is that the pump rotates as much as the engine or motor, and the bearings and other parts wear more, which shortens the service life of the pump. The direct-drive high-pressure cleaner directly transmits the vibration of the engine or motor to the pump. Moreover, the faster pumps of the direct-drive high-pressure cleaners rotate too fast, so that they cannot suck water from the water tank well. However, when water is forced into the pump, they tend to work very well, just like connecting it to a hose. To sum up: 

● Compact Design
● Lower Acquisition Cost

● Shorter Lifespan
● Unable to get water from a tank or standing water source

Water Garden Applications

Over the past decade, direct-drive pumps have been the backbone of the pond and water garden industry. These pumps are powerful and can produce large amounts of flow even when pumped to heights above 2-3 meters. Most direct-drive pumps are made of metal and are heavier than their magnetic drive pumps. Direct-drive submersible pumps are ideal for very long streams or very high waterfalls. The extra power they provide greatly increases the visual effect of larger water features. 

Of course, having a higher flow rate at a higher altitude will bring higher energy costs. Direct-drive pumps usually consume up to three times the power of a similar capacity hybrid magnetic drive pump. In areas with particularly high electricity rates, the operating costs of these pumps may exceed the user's burden. Direct-drive drive pumps are still the pump of choice for most professional pond installers.

Direct-drive pumps require bearings and pump seals, which will eventually fail. According to the experience of many pond installers, the failure rate of direct-drive pumps is faster than similarly mixed flow pumps. These type of pumps require a certain amount of back pressure to achieve their maximum capacity. This means that the actual service life of the pump is longer and it performs better when the pump reaches about half of its maximum lifting capacity (head pressure). Using a direct-drive pump on a ground filter or water flow will require the use of a flow reducer to prevent premature damage to the pump seals and bearings.

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