Introduction

The development of high-pressure cleaners has paralleled the development of high-pressure pumps. As higher pressure, lightweight, affordable pumps became available, high-pressure cleaners evolved from steam cleaning equipment.

Pumps come in a great variety of sizes and types. Only a few pump types are commonly used in high pressure cleaning applications. High pressure cleaning requires a pump, which produces a relatively high pressure, usually in excess of 1000 psi, with a relatively low flow, generally less than 5 gpm. Additionally a pump used on a cleaner must be light enough for a certain amount of portability and economical enough to manufacture that the cleaner can be sold for a competitive price.

High-pressure pump types

Since high-pressure cleaners began gaining popularity in the late 1960’s and early 1970s advances in high pressure pumps have driven advances in the development of high pressure cleaning equipment. The early machines often were fitted with piston cup pumps like those shown at top right. The high-pressure ceramic plunger pump shown at right is relatively lightweight and can be mass-produced at a reasonable cost. Direct drive pump designs such as those shown at far right have become quite common.

A Brief History of High Pressure Pump Development

An Evolution
Pump designs used in high pressure cleaning have evolved over the years as new applications of technologies offered new ways to meet these requirements. Today, most pumps in service on high-pressure cleaners fall into one of three major categories, and each of these categories marks a step in the evolution of the pumps used in the high pressure cleaning equipment industry.

Steam Cleaners

Steam cleaners, the first cleaning equipment type to become commercially available, had modest pumping requirements. Most of the force propelling water out of the steam nozzle came as the result of vapor expansion within the steam nozzle as superheated water was released to atmospheric pressure and steam was released.

The pump’s primary purpose was to provide sufficient pressure to keep water in liquid form inside the system. At the optimum steam cleaning temperature of 325 degrees, only about 80 psi is required to keep water in its liquid state. Consequently the first steam cleaners used pumps that developed pressures in the 100-psi range. This allowed the use of a variety of pumping unit types, none of which had to be constructed to withstand particularly high pressures.

Cleaner designers began using pumps that were somewhat more powerful than was necessary to allow water heating to the desired temperature. These pumps produced outputs in the vicinity of 250 psi or more. Stream cleaners using these larger pumps were referred to as hydraulically assisted steam cleaners. The additional pump pressure added to the impact of water droplets propelled from the steam nozzle by the force of vapor expansion alone, as had previously been the case. Diaphragm pumps became popular in some steam cleaner designs because they were capable of pumping harsh acids through the system for de-scalingwithout damage to the pump.

True Pressure Cleaners
As lightweight pumps capable of higher pressures, became available, high pressure cleaning without the need for vapor expansion became a reality.

Using only pump pressure to propel the water allowed use of lower temperatures. The same volume of water could be heated to the desired cleaning temperature using less fuel.

Most of the early high-pressure cleaners used pumps producing around 500 psi. The most common pump design used was the piston cup pump in which the inlet check valve was part of the piston assembly and the packing moved along with piston movement through the cylinder.

Better manufacturing techniques and more painstaking design and machining brought about piston pump pressures in the 1000-psi range. But the search for higher pressures in a lightweight pump continued. This research and development led to the production of ceramic plunger pumps which cold be machined to closer tolerances and produce higher pressures than the piston cup pumps. The first plunger pumps looked much like piston pumps, but the plunger pump design quickly matured into a simple, easy-to-service pumping unit.

Driving the Pump

For most of the history of the high pressure cleaning equipment industry, belts and pulleys have driven pumps. Pumps were not necessarily designed to operate at the same speeds as available motors or engines, and blest drives allowed reduction of pump speeds to lower rpm levels that cased less wear than operation of pumps at motor or engine speeds.

The increased use of four-pole electric motors with 1725 rpm shaft speeds brought pump and motor speeds closer together and made directly driven pumping units a viable alternative. Additionally, newer pumps could operate at higher speeds and a plateau of compatibility was reached.

The use of direct-drive ceramic plunger pumps represented an adaptation of an existing pump design. The simplest form of direct drive was to attach the pump shaft directly to the motor shaft pressed steel plungers into the pump cylinders for the compression or discharge stroke and high-tension springs pushed the plungers back out of the cylinders on the suction or inlet stroke. This is similar to the operation of an automobile camshaft and cylinder valves. And, in their pure form, swash-plate pumps have long been used in automotive applications. More pump designs of this type are becoming available in the industry.

The Three Major Pump Types Used In High Pressure Cleaning Today
Today, three pump types are in general service in high-pressure cleaners:
· Crankshaft driven ceramic plunger pumps, which make up the majority of pumps used in equipment produced today and in recent years.
· Wobble or swash plate drive pumps with stainless steel or ceramic plungers. These pumps are most common on cleaners produced by major European manufacturers.
· Piston cup pumps, which were used on much of the older cleaning equipment that is still in service.

The Same Principles, The Same Requirements

All three-pump types have somewhat different characteristics but all operate on the same basic principles and have similar or analogous components. Consequently, care and service of all three types are similar as well. Similarities outweigh the differences between these pump types. Nevertheless, pump designs may differ vastly in appearance and a wide variety of pump models, which fit the relatively narrow requirements of high pressure cleaning, are available.

All are relatively lightweight and inexpensive to produce. All move water through the straight-line action of plungers or pistons. All incorporate the same basic components: a crankcase, a manifold, check valves, cylinders, plungers or pistons, packing and seals. All pump types used in the industry will perform better when properly operated, maintained and serviced.