A PULSATION DAMPER FOR ABSORBING PRESSURE PULSATIONS IN A HIGH PRESSURE HYDRAULIC SYSTEM.

Abstract: In order to absorb disturbing pressure pulsations in a high pressure hydraulic system, the transport pipe (15) between source (10) and consumer is cut in at least one place and a damper (16) is mounted. The damper comprises at least one damper pipe (17, 18), having a larger diameter than the transport pipe (15), without normally exceeding an inner diameter of 70 mm. If two or more parallel damper pipes are used, these are connected by means of a part (19) of the long intervening pipe, so that a compact unit is obtained, suited to local conditions.

Description: A PULSATION DAMPER FOR ABSORBING PRESSURE PULSATIONS IN A HIGH PRESSURE HYDRAULIC SYSTEM. Disturbing pressure pulsations can develop within high pressure hydraulic systems, and are usually caused by noise sources like e.g. pumps, hydraulic motors and control de¬ vices. Different arrangements have been proposed for reducing these pressure pulsations, but these have all been either expensive or complicated, not the least ' because the prevai¬ ling high pressure demands fulfillment of construction re¬ gulations and prevents the use of damping chambers or con¬ tainers used for other damping purposes. The object of this invention is to propose a damping device that functions better acoustically than prior dam¬ pers in this field, is simple to mount and to use, and is suitable for mass production, and easily adaptable to various amounts of installation space. The invention enables a compact joining of damper and pump. In a damper according to the invention the normal transport pipe from the source of pulses is cut in at least one place, and is replaced by a damper chamber having a larger diameter than the transport pipe, and the invention is characterized in that the damper chamber is a pipe having an inner diameter less than the lower limit for pressure vessels and having a length substantially corre¬ sponding to one quarter of the wave length of the basic tune in the system, in operation. Preferably at least two substantially like damper chambers are arranged in series, and interconnected by a pipe, having a length substantially equal to one quarter of the wave length of the basic tune. The connecting pipe preferably has a smaller diameter than the transport pipe. The damper chambers are advantageously located in parallel relationship, the connecting pipe being bent in the space outside the chambers. The part of the connecting pipe joining a damper chamber preferably continues into the later. The transport pipe advantageously joins the damper chamber substantially at right angle to its longitudinal axis, and at a distance from one of its closed ends. The portion of the transport pipe extending between the source of pulses and the damper chamber advantageously is a small part of the total transport path. The invention will now be described in the following and by reference to the accompanying drawings, wherein. Fig. 1 is a diagram showing the relationship between noise level and frequency within a high pressure hydraulic fluid pipe and Fig. 2 illustrates one embodiment of the damper according to the invention. The hydraulic system illustrated in Figure 2 comprises a pump 10 of the axial piston type with several pistons working in parallel, e.g. nine pistons driven b an elec¬ tric motor 11. The flow from the pum reaches a consumer o'f fluid pressure, via a filter 12, which is mounted in a frame containing a tank 13 for return fluid from the con¬ sumer. The fluid is drawn to the pump 10 via conventional means 14. A transport pipe 15 extends from the pump to the hydraulic machine via a damping device according to this inventio . The transport pipe 15 is designed for the pressure and flow demanded by the machine, and comprises a middle part 15a between the pump and the damper device and a part 15b between the later and the filter 12. The inner diameter of the pipe can for example be 25 mm. The damper chamber shall have a bigger diameter than the transport pipe, and it must enclose a certain volume. For cost saving reasons it is advantageous to be able to use a high pressure pipe. The inner diameter thereof must however not exceed .the lower limit for what is to be regar¬ ded as a pressure vessel. This means that the inner diameter, generally, shall not exceed 70 mm. A chamber with bigger diameter and the required volume will be expensive to manufacture, and its end walls may tend to "flutter", making the hydraulic system vibrate longitudinally. The damper 16 shown, comprises two damper pipes 17 and 18, having an inner diameter of no more than 70 mm. These are connected by means of a long pipe 19, preferably having a slightly less inner diameter than the transport pipe 15. ' The smaller pipe 19 can easily be bent to any suitable shape, so that the damping pipes 17 and 18 can be suitably located in relation to adjacent components. If needed, also the damping pipes 17 arid 18 can be bent. The pressure pulses present in a high pressure hydrau¬ lic system depends on several factors, e.g. the ' design and speed of the pump or the machine and the working pressure, and it is evident that the size and design of the damper 16 can be varied in accordance to local circumstances and needs of damping. Figure 1 illustrates measured noise values in dB for different vibration frequencies, Hz. The upper curve 20 corresponds to values in an undamped system, while the low¬ er curve 21 shows values for a system incorporating a dam¬ per according to the invention. Each throw of the pump axle results in a pressure pulse in the hydraulic fluid with a base frequency 22, but be¬ cause there are nine pistons working with a certain phase overlap, this means that the resulting signal will be. smoothed. Certain peaks 23 do however appear within this signal caused by the compression of the fluid due to the increase in fluid pressure, and subsequent sudden compen¬ sation. Primarily these pressure peaks cause the irritating noise, with the base frequency (f_) 22 and its overtunes. The acoustic velocity within a hydraulic system of steel pipes is about 1350 m/sec for oil, compared to about 350 m/sec in air or gas. The wavelengths will therefore be about four times larger in a hydraulic system, which allows for the use of interference absorption within the damper, if this is made sufficiently long. As have been mentioned above, the pressure pulsations present in the system depend upon several factors related to design. The length and volume of the damper can there¬ for vary between wide limits. An important parameter is the quarter wavelength of the base tone, /4 A/4 = 1350 f = 22 (according to 4 x f Figure 1) Example; f = 200 Hz gives -' 4 = 1.7 mm The length of the connector pipe 19 is preferably se¬ lected as about the quarter wavelength. The length L of one damper pipe 17, 18 is preferably selected as 2/3 of the pipe 19. Alternatively can longer pipes be selected if consideration is taken for a suitable interference effect, so that a good absorption is obtained in the necessary range of frequencies. At a larger flow than about 400 1/min, longer pipes are selected in order to permit sufficient volumes and still keeping small dimensions in the damper pipes 17 and " 18. The reasons for selecting long pipes are: 1. The internal diameter of the pipes can be kept small, which makes it easy to make a strong design. 2. The muting of interference waves must be as efficacious as possible. 3. Resonances in the pipe-volume-pipe-volume-pipe-system (15a-17-19-18-15b) shall normally lie below the base frequency. Longer pipes will reduce the need of volume, because the frequency is kept constant. During normal dimensioning the lengths used are less than half the quarter wavelength. The length of the connector pipe 19 can vary in rela¬ tion to the frequencies which shall be muted and it is not necessary for the ends to reach equally far into the two damper pipes 17, 18. These ends opposite from the connector pipe 19 are blocked by gable walls 24, against which the waves are re- fleeted at maximum pressure. The connection of the trans¬ port pipes 15a, b are made at right angle to the longitudi¬ nal axis of the damper pipes, and at a distance "b" from adjacent gable 24, which is selected in relation to expec¬ ted reflection waves. The embodiment illustrated and described above is but one example of the invention, which can be modified in many details within the scope of the accompanying claims. In certain cases it can be .sufficient with only one damper pipe 17, whereby the parts 15a, b of the transport pipe can be axially connected to the end walls of the damper pipe. In other cases it may be suitable with more than two damper pipes. One simple arrangement is to double the illustrated embodiment with two damper pipes, i.e. four damper pipes with a very high damping capacity. The damper pipes need not have equal length, and in order to reduce the length of the transport pipe part 15a, one end of the damper pipe 17 can be bent and affixed directly to the pump 10. Several location alternatives are possible. When the flow is small it is possible to divide one damper pipe by means of a partition wall into two chambers interconnected through the partition wall by a small pipe corresponding to the connection pipe 19. This pipe prefer¬ ably is helically wound to get the desired length into the shorter larger pipe. Depending on the available space the damper pipes 17, 18 can be arranged at different angles to each other. The bent part of the connection pipe 19 can be partly replaced by a piece of hydraulic hose.

Claims: AMENDED CLAIMS [received by the International Bureau on 16 August 1985 (16.08.85); original clai 1 amended; other claims unchanged (1 page)] 1. A pulsation damper for absorbing pressure pulsa¬ tions from a source of pulses, e.g. a pump (10), in a high pressure hydraulic system, in which the normal transport pipe (15a, b) from the source (10) of pulses is cut in at least one place, and is replaced by a damper chamber having a larger diameter than the transport pipe (15), c h a ¬ r a c t e r i z e d in that the damper chamber (17, 18) is a pipe having an inner diameter less than the lower limit for pressure vessels and having a length substantially corresponding to one sixth of the wave length of the basic tune in the system, in operation. 2. A damper according to claim 1, c h a r a c ¬ t e r i z e d in that at least two substantially like damper chambers (17, 18) are arranged in series, and inter¬ connected by a pipe (19), having a length substantially equal to one quarter of the wave length of the basic tune. 3. A damper according to claim 2, c h a r a c ¬ t e r i z e d in that the connecting pipe (19) has a smaller diameter than the transport pipe. 4. A damper according to either of claims 2 or 3, c h a r a c t e r i z e d in that the damper chambers (17, 18) are located in parallel relationship, the connecting pipe (19) being bent in the space outside the chambers. 5. A damper according to any of the preceding claims, c h a r a c t e r i z e d in, that the part of the connec¬ ting pipe (19) joining a damper chamber (17) continues into the later. 6. A damper according to any of the preceding claims c h a r a c t e r i z e d in, that the transport pipe (19) joins the damper chamber (17, 18) substantially at right angle to its longitudinal axis, and at a distance from one of its closed ends.

Inventors: ALVEN JAN, WADMARK BO, ALVEN, JAN, WADMARK, BO
Applicants: INGEMANSSONS INGENJORSBYRA AB, INGEMANSSONS INGENJOERSBYRAO AB
Application year: 1985
Main classification: F16L55
IPC codes: F04B11, F16L55