Reciprocating pump

Abstract: The invention relates to a reciprocating pump provided with pump sections (l₁,l₂,l₃)in which a discharge stroke and a suction stroke are alternately produced by the reciprocating motion of an action element, such as a bellows (7), a diaphragm or the likes, and, in particular, relates to a reciprocating pump which comprises a plurality of pump sections (l₁l₂,l₃) each having the discharge outlet and suction inlet being communicated with common discharge and suction passageways respectively and a drive-control means (22) for drive-controlling the pump sections in such a manner that by differentiating the time to start the discharge or suction stroke, the discharge stroke may be produced in at least one pump section at the time to change-over the strokes or the time of the suction stroke in at least on pump section other than the above mentioned pump section. According to this reciprocating pump, the fluid discharge from the common discharge passageway (16) is not intermittent but is substantially continuous with the result that the occurrence of a pulse pressure is greatly reduced.

Description: FIELD OF THE INVENTION The invention relates to a reciprocating pump, such as a bellows-type pump or a diaphragm pump, provided with pump sections in which a discharge and suction strokes are alternately produced by the reciprocating motion of a pump action element, such as a bellows or a diaphragm. PRIOR ART It is known that a bellows-type pump or a diaphragm pump provided with one pump section (hereinafter called "the 1st conventional pump") or a pair of pump sections interlocked each other (hereinafter called "the 2nd conventional pump") has been generally used. In the 1st conventional pump, discharge and suction strokes are alternately produced by the reciprocating motion of a pump action element, such as a bellows. In the 2nd conventional pump, the discharge outlet and the suction inlet of each pump section are communicated with respective common discharge and suction passageways thereof, and pump action elements of both the pump sections are interlocked each other so that a discharge stroke produced in one pump section coincides with a suction stroke produced in another pump section. In the 1st conventional pump, however, since a discharge stroke is intermittently produced, the pumped fluid inevitably pulsate, and pulse pressure occurs on the discharge side. In the 2nd conventional pump, since the change from a discharge stroke to a suction stroke in one pump section coincides with the change from asuction stroke to a discharge stroke in another pump section, discharge strokes appear to be continuously produced, however, the coincidence of stroke changes in both the pump sections cause high pulse pressure to be created at the time of such stroke changes as in the above description. The occurrence of such high pulse pressure on the discharge side give rise to many problems. For example, due to an impact resulting from the pulse pressure, additives can be peeled from the interior surface of piping to accumulate of impurity therein, holes in a filter can be enlarged to lower the capture rating of the filter, or pipe connections can be loosened to cause the occurrence of a leakage. In addition, conventionally, a means to reduce pulse pressure has been disposed on the discharge piping side, but this only gives rise to the further problem of uselessly increasing pumping equipment size and complicating its construction. It is known from EP 0,212,728 to provide a multi section complex pump where the movement of the displacer rods are monitored by a recording device which then feeds a signal to a control mechanism which then controls the piston movement in a so-called oblique sinusoidel movement. This is a somewhat complex solution to the problem. SUMMARY OF THE INVENTION One object of the invention is to provide a reciprocating pump that can reduce pulse pressure as low as possible by enabling a plurality of pump sections to perform substantially continuously and unceasing discharge from a common discharge passageway in a manner which is simpler than the complex solution of the prior art. Another object of the invention is to provide a reciprocating pump reduced in size and simplified in construction by allowing the pump to have the function of lowering pulse pressure and thus by eliminating the need to employ a means, such as an accumulator, for reducing the pulse pressure in the pipings on the discharge side. The above mentioned objects are attainable by providing a reciprocating pump which comprises: a plurality of pump sections (1₁, 1₂, 1₃,) in each of which a discharge stroke and a suction stroke are alternately produced by the reciprocating motion of a pump action member such as a bellows, a diaphragm or the like each of which pump sections has a suction inlet incorporating a check valve and a discharge outlet including a check valve, in each of which the discharge outlet and the suction inlet communicate with common discharge and suction passageways respectively, and further comprises sensing devices for sensing the position of movement of each pump section and a control mechanism for controlling the movement of the pump sections, characterised in that each said sensing device is an end of stroke sensor arranged to detect the starting time and the ending time of the discharge stroke and the suction stroke respectively, and that the control mechanism is arranged to provide a delay time t between the start of the stroke of each successive pump section which can be set at any position within a relationship T/n ≦ t < T where T is the time from the start of a discharge stroke to the end of that stroke as measured by the sensing device, and n is the number of pump sections. With this arrangement by simply measuring the position of the end of each stroke and then providing successive time delays a less complex solution is achieved. In a pump of this type, even during the change of strokes and the performance of a suction stroke in one pump section, a discharge stroke is produced in at least one of other pump sections. Therefore, fluid is continuously pumped out of the common discharge passageways by at least one of the pump sections. This means that the action of discharging fluid from the pump as a whole is continuously maintained, and pulse pressure can be greatly reduced as compared with the case of an intermittent discharge action. In a preferred embodiment a plurality of composite pump comprised of a pair of pump sections connected and interlocked each other are arranged such that, while a discharge stroke is produced in one of the two, a suction stroke is produced in the other. In this case, "t" that is a difference in the starting time for a discharge or suction stroke between composite pump sections and is controlled by a drive-control means is preferably set at T/N in which T is the time from the start of a discharge or suction stroke to the end with composite pump sections and N is the number of the composite pump sections as employed. Other objects, features, aspects and advantages of the present invention will become apparent upon consideration of the following detailed description of the invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of a reciprocating pump of the invention and is a transverse sectional view taken along line I-I of FIG. 2. FIG. 2 is an enlarged vertical sectional front view taken along line II-II of FIG. 1. FIG. 3 is a vertical front view similar to that of FIG. 2 and shows a modification of pump sections. FIG. 4 is a driving time chart of pump sections. FIG. 5 to 7 are graphs showing respective experimental results on reducing pulse pressure. DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIGs. 1 to 5, a detail description will be made on the embodiment illustrated therein as follows: The embodiment relates to an example of the application of the invention to an air-operated pump of bellows-type. For purposes of illustration, the front-rear and right-left directions to be stated in the following description are shown in FIG. 1 as the upper-lower and right-left directions respectively. In the embodiment, the reciprocating pump of bellows-type is provided with No. 1 to 3 composite pump sections 1₁, 1₂, 1₃ arranged side by side in the front-rear direction and a drive control means 2 for driving and controlling them, as shown in FIG. 1. Each of the composite pump sections 1 comprises a pair of pump sections 1a operatable in association with each other and is disposed on opposite right-left hand sides. The pump section 1a comprises six pump chambers which are arranged in the form of two chambers placed in the transversal direction and three ranks of the two chambers in the front-rear direction and are partitioned in the inerior of the pump casing 3 by pump head walls 4 and cylinder walls 5, and cylindrical bellows 7 with the bottom each of which is disposed in the pump chamber 6 and works as a pump action element which is retractable and stretchable in the right-left direction. As illustrated in FIGs. 1 and 2, each of the bellows 7 hermetically divides the interior of the pump chamber 6 into a pump action chamber 6a within the bellows and a pump operation chamber 6b outside the bellows by making an annular clamp plate 9 securely press a opening peripheral edge portion 7a onto the pump head constituent wall 4 while maintaining the condition that annular recess formed in the portion 7a is filled with an adequate gasket 8. Moreover, to a bottom portion 7b of each of the bellows 7 is secured an action plate 11 by an annular clamp plate 10. In each of the composite pump sections 1, the bellows 7, 7 of the pump sections 1a, 1a on the right and left sides are interconnected with each other by a plurality of connecting rods 12 (only one is shown) in such a manner that the bellows 7 on one side is contracted while the bellows 7 on the other side is stretched as shown in FIG. 2. The length of the connecting rod 12 is so determined that the bellows 7 on one side is stretched to the utmost limit when the bellows 7 on the other side is contracted to the minimum. Both ends of each rod 12 are secured to the action plates 11, 11 with its middle part penetrating the pump head wall 4. On the penetrating part is disposed a sealing member 13, such as an O-ring, which seals and stops the pump action chambers 6b, 6b on the right and left sides from communicating with each other while, at the same time, permitting the rod 12 to slide therethrough. In the pump head constituant wall 4 are formed not only a discharge passageway 14 and a suction passageway 15 which are extended in the front-rear direction but also discharge outlets 14a ... and suction inlets 15a ... which open to the pump action chambers 6a. The discharge outlet 14a ... and suction inlet 15a ... are communicated with the discharge passageway 14 and the suction passageway 15 respectively. Moreover, to the discharge passageway 14 and the suction passageway 15 are connected pipings 16 on the discharge side and pipings 17 on the suction side respectively. Each pump section 1a is provided with a leakage sensor 18 for detecting fluid leakage from the pump action chamber 6a to the pump operation chamber 6b. Each discharge outlet 14a and each suction inlet 15a are provided with a check valve 19 for discharge and a check valve 20 for suction respectively. As shown in FIG. 2, the check valve 19 for discharge permits the flow out of the pump action chamber 6a into the discharge passageway 14 during the discharge stroke, checking the cross current from the discharge passageway 14 to the pump action chamber 6a during the suction stroke, and the check valve 20 for suction permits the flow from the suction passageway 15 into the pump action 6a during the suction stroke, checking the cross current from the pump action chamber 6a to the suction passageway 15 during the discharge stroke. Both the check valves 19, 20 can be an integrated construction if required as shown in FIG. 3. The drive-control means 2 is provided with air drive mechanism 21 ... for driving each composite pump section 1 and further with a delay control mechanism 22 for delaying and controlling the action of the former mechanism. Each air drive mechanism 21 permits both the bellows 7, 7 to make a reciprocating motion by delivering a pressured air at a fixed interval through air delivery passageways 21a, 21a alternately into the pump operation chambers 6b, 6b on the right and left sides of the composite pump section 1. The air drive mechanism 21 comprises a change valve for changing-over the air delivery passageways 21a, 21a alternately to the delivery port and the air exhaust port and a pulse timer for setting the change-over time. In each composite pump section 1, as shown in FIGs 1 and 2, for example, delivery of the pressure air into the pump operation chamber 6b on the left side exerts pressure to allow the bellows 7 on the left side to make the contracting action , the fluid within the pump operation chamber 6a being then made to flow through the discharge port 14a toward the discharge passageway 14. The discharge stroke in the pump section 1a on the left side is then started. Concurrently with this operation, the bellows 7 on the right side is stretched , the fluid being made to flow from the suction passageway 15 into the pump operation chamber 6a through the suction inlet 15a. The pump section 1a on the right side is made to start the suction stroke. The air within the pump operation chamber 6b on the right side is discharged at this time out of the air delivery passageway 21a. When the discharge stroke in thepumpsection 1a on the left side and the suction stroke in the pump section 1a on the right are ended, the change valve is actuated by the pulse timer as described above, the delivery and discharge of the pressure into and from both the pump operation chambers 6b, 6b being made to change-over, and the discharge stroke in the pump section 1a on the right side as well as the suction stroke in the pump section 1a on the left side being started. The composite pump sections 1 ... to be driven by the air drive mechanism 21 ... are controlled by the delay-control mechanism 22 such that the time to start driving one composite pump section 1 is made to differentiate by a fixed length of time from the time to start another composite pump section 1. The delay-control mechanism 22 detects the starting and ending time of the discharge and suction strokes in the No. 1 composite pump section 1₁ and controls the time to start the discharge and suction strokes in the composite pump sections 1₂, 1₃ in such a manner that, with the time to start the discharge and suction strokes in the No. 1 composite pump section 1₁ being the standard, the starting of the discharge and suction strokes in the No. 2 and 3 composite pump sections 1₂, 1₃ are sequentially delayed by a fixed length of time. The detection of the time to start and end the discharge or suction strokes is, as shown in FIG. 2, performed by sensors 22a, 22a which are disposed on the walls of composite pump section 1₁ on the left and right sides and which are operated by both operating plates 11, 11. A time of differentiation in the starting time of the discharge or suction stroke between No. 1 to 3 composite pump sections 1₁, 1₂, 1₃ is set at T/N = T/3 in which T is time from the start of the discharge stroke or the suction stroke to the end and is measured by the sensors 22a, 22a and N is the number of the composite pump sections 1 as employed. Therefore, No. 2 composite puma section 1₂ is so controlled as to start the discharge stroke T/3 after No. 1 composite pump section 1₁ has started the discharge stroke. Further, No. 3 composite pump section 1₃ is so controlled as to start the discharge stroke 2T/3 after No. 2 composite pump section 1₂ has started the discharge stroke. Due to the differentiation in the starting time of the discharge stroke between No. 1 to 3 composite pump sections 1₁, 1₂, 1₃, one pump section 1a on one side of one composite pump section 1 is capable of carrying out the discharge operation even when another composite pump section 1 is at the time of changing-over, as shown in Fig. 4. Hence, the discharge from the common discharge passageway 14 is, in substance, continuously carried out and the pulse pressure is greatly lowered. FIG. 4 shows a driving time chart with regard to the pump 1a on one side of each composite pump section 1. The effect of reducing pulse pressure by means of delay-control as described above was experimentally confirmed as follows: A pump of bellows-type as described in the foregoing embodiment was operated with a fresh water at 25°C used as the discharge fluid and under conditions that the pressured air delivered to each pump operation chamber 6b was 4 kgf/cm², a stroke produced in each composite pump section 1 was 50 spm (T = 0. 6 sec.), and a delay time t among composite pump sections 1₁, 1₂, 1₃ was set at 0.2 sec., the discharge pressures were measured along with the passage of time, and the results as shown in FIG. 5 were obtained. Pressure differences due to pulsation, that is, pulse pressures were as little as about 0.5 kgf/cm². As a comparative example, the No. 1 to 3 composite pump sections 1₁, 1₂, 1₃ were operated under the same conditions as above but without the application of delay-control as described above. The discharge pressures were measured when, at first, the starting time of the discharge stroke for all the three No. 1 to 3 composite pump sections 1₁ to 1₃ was the same without differentiating the starting time between the composite pump sections 1, and next when only No. 1 composite pump section 1₁ was operated. FIG. 6 shows the results of the former case, and FIG. 7 shows the results of the latter case. The pulse pressure was about 1.5 kgf/cm² in either case. Material formed into component members of the pump of bellows-type in the foregoing embodiment is fluororesin agent that is abundant in chemical resistance, such as PTFE, PFA, CTFE, etc. It is not intended to have the reciprocating pump of the present invention limited to the foregoing embodiment, and modifications may be appropriately made without departing the fundamental principle of the present invention. For example, according to the delay-control mechanism of the foregoing embodiment, the stroke starting time of No. 1 composite pump section 1₁ is considered the standard, with the stroke starting time of No. 2 and 3 composite pump sections 1₂ and 1₃ being delayed sequentially. But, alternatively, it is possible to individually control the stroke starting time of each of the composite pump sections 1, thereby establishing the most optimum delay time that the conditions of the pump operation permit. It is also possible to set in advance the delay time by a timer. In general, preferably, the delay time t between the composite pump sections 1 is set at T/N as described above. However, since in each composite pump section 1, a discharge stroke is produced in one pump section 1a on one side at any given time except for at the time of changing-over the strokes, the setting of the delay time t can be made in any way as long as the time to change the strokes in one composite pump section 1 does not coincide with the time to change the strokes in another composite section 1. In this case, the number of the pump sections 1a should be preferably large. This is because the more the pump sections 1a as employed are, the smaller the pressure differences due to pulsation are. Also, the occurence of a time lag between the delay time controlled by the delay-control mechanism 22 and the actual delay time is a consideration. In the foregoing embodiment, the two pump sections 1a are interconnected with each other to form one compoiste pump section 1 and, hence, N sets of composite pump sections 1 need 2N pieces of pump sections 1a. But, alternatively, each pump section 1a can be so structured that it is driven independently of the other pump section 1a. In this case, time of differentiation in the stroke starting time of the pump section 1a is so determined that at least one pump section 1a is in the discharge stroke when at least one pump section 1a other than the above mentioned pump section 1a is at the time of changing-over strokes or in the suction stroke. In the case that the number of pump sections 1a is 'n' pieces, the setting is theoretically possible within the range of 1.5T/n<t<T . But, this range is actually widened by the above mentioned time lag. Hence, in general, the setting may be made appropriately within the range of T/n≦t<T . Also, the means for driving the pump section 1a is not limited to the above described drive mechanism 21 which can deliver and evacuate the pressured air. The present invention is applicable not only to the above mentioned pump of bellows-type but also to a diaphragm pump, or the reciprocating pump of other types (e.g. a cylinder pump).

Claims: A reciprocating pump which comprises: a plurality of pump sections (1₁, 1₂, 1₃,) in each of which a discharge stroke and a suction stroke are alternately produced by the reciprocating motion of a pump action member such as a bellows, a diaphragm or the like each of which pump sections has a suction inlet incorporating a check valve (20) and a discharge outlet including a check valve (19), in each of which the discharge outlet and the suction inlet communicate with common discharge and suction passageways respectively, and further comprises sensing devices (22a) for sensing the position of movement of each pump section and a control mechanism (2) for controlling the movement of the pump sections, characterised in that each said sensing device is an end of stroke sensor arranged to detect the starting time and the ending time of the discharge stroke and the suction stroke respectively, and that the control mechanism is arranged to provide a delay time t between the start of the stroke of each successive pump section which can be set at any position within a relationship T/n ≦ t < T where T is the time from the start of a discharge stroke to the end of that stroke as measured by the sensing device (22a), and n is the number of pump sections. A reciprocating pump according to claim 1 characterised in that each pump section comprises a leak detector (18) for detecting fluid leakage. A reciprocating pump according to claim 1 or claim 2 in which, component members of the pump of bellows type are formed of a fluororesin that is abundant in chemical resistance such as PTFE, PFA or CTFE. A reciprocating pump according to any preceding claim in which the pump sections are arranged in pairs of sections which are connected by connecting means (12) so that each discharge stroke and each suction stroke are the same.

Inventors: FUKUMOTO TOSHIYUKI, IMANISHI RYO, FUKUMOTO, TOSHIYUKI, IMANISHI, RYO
Applicants: NIPPON PILLAR PACKING, NIPPON PILLAR PACKING CO. LTD.
Application year: 1990
Main classification: F04B11
IPC codes: F04B11, F04B43