附录AInvestigation on Pressure Impact in ConcretePumping Hydraulic System Abstract：The pressure impact in hydraulic systems of such concrete pumping machinery as trailer concrete pump，transported concrete pump，and truck mounted concrete pump，is a key factor affecting their reliability and usage lifeBased on the pressure forming principle of the oil in a hydrostatic closed pressure chamber，the mechanism of producing pressure impact is analyzed synthetically，and the theory that oil flow matches requirement， and pump displacement control harmonizes valve shifting time control，to mitigate pressure impact，is put forwardThe quantitative controlling parameters about shifting time and displacement control are introduced to realize accurate controlThe experiment investigations of pressure impact property and its control are carried through on an experimental system which is able to simulate concrete pumping conditionThe basic law that pressure impact and controlling parameters vary with working condition respectivelyThe feasibility and validity of the technology proposed in this paper to control pressure impact are confirmed.Keywords: Pressure impact；Hydraulic system； Concrete pumping machinery1 IntroductionDuring working process of such concrete machinery as trailer concrete pump，transported concrete pump，and truck mounted concrete pump，two oil cylinders drive two concrete delivery cylinders respectively，and quickly switch direction with the possible highest frequency of more than 30 times per minute，which generates serious hydraulic impactIt is an important factor resulting in bad performance and low use reliability of the machine， and vibration，noise and overheating etcso its a key of improving concrete pumping machinerys reliability to gain a mastery of pressure impact property in concrete pumping hydraulic system and its controlling technologySuch technological measures as follows were taken to reduce pressure impact：(1)installation of a hydraulic accumulator or unloading valves，(2) change of sliding spools structure，(3)control of the switching speed of sliding spool，etc1Though these measures play an important role in absorption of pressure surges，there are obvious limitations， and they are passive measuresLiterature.2. investigated the switching process of concrete pumping hydraulic system，and put forward active measure of regulating oil pumps displacement to reduce pressure impactLiterature3studied the intrinsic relationship between shifting time and pressure impact，and proposed a new concept of optimal shifting timeTherefore，in this paper, experiments were conducted to find out pressure impact forming law， and both oil pumps displacement and directionalcontrol valves shifting time were controlled simultaneously to seek optimal control scheme for effective reduction of pressure impact2 Experimental principleThe pressure variation of the oil in a pressure chamber depends upon the difference between volumes of the oil flowing in and out the chamber2Its obvious that effective reduction of this difference is of positive significance for depressing pressure impact As far as concrete pumping hydraulic system is concerned, the pressure impact resulting from the main oil cylinders stroke terminal lies upon the suitability of shifting time to a great extent3So its feasible and effective for absorbing pressure impact to accurately control oil pumps displacement according to hydraulic systems requirement，and combine it with shifting time control techniqueWhat is shown in Fig.1 is the principle drawing of the experimental system sued to study characteristics of pressure impact in concrete pumping hydraulic system and its controlling techniquesThe main oil pump(1)is a swash-plate type axial piston pump，which is provided with the function of constant horsepower control。negative flow contr01The pressured oil used to contr01 oil pumps displacement comes from tilting systemIn this controlling oil line，a 3-way,2-position directional valve(11)with one solenoid and a pressure reducing valve(12)are installed in seriesWhen the solenoid of valve(11)is de-energized，the pressured oil from tilting system is stopped，and the pressured oil in the displacement control device of oil pump(1)is introduced into oil reservoir simultaneously by the valve(11)Here，the oil pressure in the displacement control device is zero or very low，the oil pumps displacement can come to maximumOn the other hand，when the solenoid of valve(11)is energized，the pressured oil coming from tilting system is introduced by the valve(11)，and is decompressed by pressure reducing valve (12)，and comes into the displacement control device，so 8s to make oil pumps displacement be reduced to minimum or zero.Two hydraulic cylinders(6.1,6.2)are connected in series，and four check valves and four throttle valves，which perform the functions of suction and cushioningare installed on the cylindersTwo n