The present invention generally relates to diaphragm metering pumps for delivering controlled amounts of a liquid from a source of supply to a process stream or to another vessel. More particularly, it relates to a new and improved diaphragm metering pump having a versatile modular construction including a separated eccentric and drive system providing improved durability, as well as other advantageous hydraulic control features.
Diaphragm metering pumps are known and used for transferring fluids from one place to another. Generally, diaphragm pumps include a pumping head area including a product chamber and hydraulic chamber separated by a displaceable diaphragm member. The inlet and exit to the product chamber are provided with one-way check valves. As the diaphragm is displaced toward the hydraulic side, the exit check valve closes under reduced pressure, the inlet check valve opens and fluid is drawn into the product chamber. Thereafter, as the diaphragm is displaced from the hydraulic side toward the product side, pressure increases on the fluid in the product chamber, closing the inlet check valve, opening the outlet check valve, and forcing fluid in the product chamber out of the exit. In continuous operation, a diaphragm pump pumps fluid through the product side in a pulsed manner.
Diaphragm displacement is achieved by varying the pressure of the hydraulic fluid on the hydraulic side through the operation of a reciprocating piston disposed in fluid communication with the hydraulic chamber. Proper long-term operation requires that the diaphragm be hydraulically balanced. Excess pressure on either side of the diaphragm can lead to irregular pumping action and excess displacements of the diaphragm, which may cause catastrophic failure of the diaphragm or shortened use life. A frequently used method for preventing excess displacements of the diaphragm has been to provide contoured dish plates on the product and hydraulic side of the diaphragm to positively limit displacement of the diaphragm by providing a physical barrier to further travel.
Prior efforts to provide a hydraulically balanced diaphragm pump have included the use of a spring-loaded pressure relief valve disposed in fluid communication with the hydraulic cavity. The pressure relief valves are designed to open when the pressure level of the fluid in the hydraulic chamber exceeds a predetermined value. The pressure relief valve opens to remove some hydraulic fluid from the hydraulic chamber to reduce the pressure therein. This prevents undesirable overdisplacement of the diaphragm toward the product side during pumping.
In addition, if the volume or pressure of the hydraulic fluid in the hydraulic chamber on the suction stroke of the piston is too low, the diaphragm can be displaced an excessive amount into the hydraulic chamber. In these circumstances, additional hydraulic fluid should be introduced into the hydraulic chamber to balance the diaphragm. Pressure sensitive valves are often used for this purpose. It has been proposed to provide a poppet valve located on the hydraulic side dish plate, which is effective to add make-up hydraulic fluid to the hydraulic chamber when displacement of the diaphragm becomes large enough to physically contact and press against the poppet valve. These mechanically actuated poppet valves are useful but a major disadvantage of prior art pumps is that the poppet valves are not accessible without disassembling the pump and many of the sealed connections therein. Moreover, no detectable information as to the condition of these valves is provided in most systems, so proper functioning of the valve is hard to discover or diagnose.
Another factor which may influence hydraulic balance in the system is the development or presence of gas in the hydraulic fluid on the hydraulic side of the diaphragm. The presence of gas in the hydraulic chamber may lead to irregular pumping action. For example, the action of the piston may compress a gas present in the hydraulic chamber rather than driving the diaphragm. Accordingly, an air bleeder valve is usually provided in an upper portion of the hydraulic chamber. The air bleeder valve may be provided in the form of a shuttle check valve which permits discrete volumes of air or fluid to be removed from the hydraulic chamber on each forward compression stroke of the piston to maintain the hydraulic cavity air bubble free.
A major problem with prior efforts for providing hydraulically balanced diaphragms has to do with priming the system for start-up. In the past, many of these valves had to be removed and hydraulic fluid manually loaded into the chamber. Thereafter, the pumps need to be operated for some time to bleed any air out of the system and permit the system to come to a hydraulically balanced state. During the start-up procedure, all of the valves may be activated and the pump typically begins operation in an unbalanced manner for a certain period of time which provides undesirable stress and wear on the diaphragm and other parts making up the system.
The drive mechanisms employed for moving the piston generally employ rotation of a shaft provided by an electric motor which is translated into reciprocating linear motion of the piston. Although various linkage arrangements between the drive shaft and the piston rod have been used, more frequently reciprocal movement of the piston is achieved by means of an eccentric cam surface provided on the rotating shaft which is combined with a spring-loaded cam follower on the piston rod. In these prior arrangements, the eccentric drive shaft has frequently been provided in an assembled form with several components mounted on the shaft. The eccentric and other elements mounted onto the shaft, given the pressures present in the system, may frequently loosen in use, requiring service.
Rotation of the eccentric shaft is frequently provided by a worm and worm gear combination wherein the worm gear is provided on the eccentric shaft. This arrangement has several disadvantages. First of all, the lubricant required for gearing connections between the worm gear and the worm require a first grade or quality gearing lubricant. The hydraulic mechanism requires a different viscosity hydraulic fluid. In the past because these two features were combined on the same shaft, a mixed fluid was used which was not completely satisfactory for either function. Moreover, when the eccentric and worm gear are on the same shaft, the bearing support spacing for the eccentric shaft is wider, causing shaft deflection stresses. As a result, bearing life may be reduced due to angular misalignment of the eccentric shaft due to deflection. These prior drive systems may suffer from premature wear and do not possess the durability desired for long-term operation of the drive system.
Another effort at providing long-term, trouble-free operation for diaphragm pumps has led to the use of a double-layer diaphragm. The use of two diaphragm layers provides better protection against contamination of the product fluid or the drive fluid in the event of a diaphragm leak or failure since it is unlikely that both diaphragms will fail at the same time. In accordance with this arrangement, the back-up diaphragm is present to prevent unwanted contamination of the fluid.
It has also been proposed to provide a leak detection system for double diaphragm arrangements wherein the gap between the diaphragms is evacuated to reduced pressure and gap pressure is monitored. If a diaphragm leak occurs, the reduced pressure in the gap will go up which may be detected by a pressure monitoring means such as a pressure gauge or switch. In prior art leak detection systems, after evacuation, the central portions of the diaphragms are drawn together which may actually seal small leaks which go detected. Accordingly, these systems are unable to detect minor leaks in the central regions of the diaphragms. In addition, rubbing of the adjacent diaphragm surfaces sometimes cause particulate debris to build up in the gap which can plug sensing channels between the gap and sensing means. If this occurs, leaks can go undetected by the monitoring system. Accordingly, a leak detection system capable of early detection of leaks anywhere on the diaphragm surface which is not susceptible to plugging is still desired.
Prior art diaphragm pumps generally provide the drive system within the pump housing which requires the housing to be undesirably large. The large size of these pumps may limit positioning and placement of the pumps, which is a major drawback to their use. In addition, prior pumps employed external tubing to connect various valves to various reservoirs and chambers, which is not only unattractive but undesirable from the standpoint of tangling, snaring, and external leaks.
In order to overcome the shortcomings of the prior art diaphragm pumps, it is an object of the present invention to provide a hydraulically balanced diaphragm pump which may be primed automatically and internally without the need to remove valves at start-up.
It is another object of the present invention to provide a hydraulically balanced diaphragm pump having a mechanically actuated hydraulic fluid make-up valve on the hydraulic side which is provided in a readily accessible cartridge for easy examination and servicing.
It is a further object of the present invention to provide a diaphragm pump wherein the condition of each of the valves employed in hydraulic balancing may be visually observed during operation of the pump.
It is another object of the present invention to provide a new and improved drive system wherein the gear reducer and pump housing are separated so that each may be lubricated by their own proper lubricants.
It is a further object of the present invention to provide a smaller diaphragm pump housing having modular features such that the drive connections may be made in several orientations to meet various height and space requirements.
It is still another object of the present invention to provide a new and improved diaphragm pump having a double diaphragm assembly which provides a method for detecting leaks in the diaphragms in use.
It is still a further object of the present invention to provide a modularized diaphragm metering pump adapted to accept either electronic or manual controls for regulating pump operation.