Constant Pressure Pump Research Articles

A RESEARCH ON THE ELECTROHYDRAULIC PROPORTIONAL CONSTANT PRESSURE AND FLOW PUMP WITH ELECTRIC FEEDBACK AND COMPENSATION

A new type of electrohydraulic proportional constant pressure and flow pump with electric feedback and compensation is introduced in this paper. The pump control system has be designed to realize constant pressure control by load pressure electric feedback and constant flow control by leakage flow compensation. A new principle of leakage flow electric compensation to pump constant flow control is proposed in this paper. Unlike conventional constant flow pump, which directly detects the load flow on the main oil-road, the additive main flow throttle loss may be avoided completely. The structure characteristics of the pump control system and experimental research results also are introduced in this paper.

Physiological determinants of Qmax in contracting canine skeletal muscle in situ.

Canine skeletal muscle preparations in situ contain varying mixtures of fast and slow fatigue resistant fibers. All vessels on the arterial side of the vascular bed in these preparations from the conduit arteries to the arterioles contribute to the vascular resistance. The vascular beds autoregulate at rest and during contractions, indicating that the effects of the surgery are minimal. Stimulation frequency and pattern, i.e., twitch or brief tetanic contractions, the force exerted, and the length at which the muscle contracts, combine to determine the metabolic rate, which in turn, establishes the blood flow at a given perfusion pressure. When blood flow is normalized for oxygen uptake, the ratio is similar for twitch and rhythmic brief tetanic contractions. The ratio stays constant over a wide range of frequencies even though the flow increases and is greater than the theoretical minimum set by the maximum arteriovenous oxygen concentration difference. The infusion of vasodilators such as adenosine results in higher flows than those obtained with 6 Hz stimulation alone, indicating the presence of a "pharmacological reserve". The peak blood flow measured with isometric twitch contractions at 6 Hz in constant pressure pump perfused muscles at the optimum length for tension development averages 19.7 +/- 1.1 ml.kg-1.s-1. The pharmacological maximum at 6 Hz averages 25.9 +/- 1.6 ml.kg-1.s-1 with an observed maximum of 33.2 ml.kg-1.s-1.

Functional significance of alpha-adrenergic receptors in mature coronary collateral circulation of dogs.

There is little information on the functional significance of alpha-adrenergic receptors in the dog's coronary collateral circulation. Accordingly, we investigated the effects of infusion of either norepinephrine (NE) or B-HT 920 (BHT), an alpha 2-adrenergic agonist, on vascular resistance of coronary collaterals in chloralose-anesthetized dogs 2-3 mo after placement of an Ameroid constrictor around the left circumflex coronary (LCX) artery. To accomplish this, the vagotomized left ventricle was autoperfused through the left main coronary ostium using a servo-controlled constant-pressure pump. Pressures of the left anterior descending (LAD) and peripheral LCX arteries were measured, and regional blood flow in LAD and LCX regions were determined with radioactive microspheres before and during NE infusion in the unblocked condition, following beta-adrenergic and beta + alpha 1-adrenergic blockade with the use of propranolol and prazosin, respectively. The same parameters were also measured before and during BHT infusion following beta-adrenergic and beta + alpha 2-adrenergic blockade with the use of propranolol and idazoxan, respectively. In the unblocked condition, NE reduced LAD, LCX, and collateral resistance by 43, 50, and 31%, respectively. After beta-adrenergic blockade, NE increased LAD resistance (29%) but did not alter LCX or collateral resistance. The increase in LAD resistance was abolished following alpha 1-adrenergic blockade. BHT increased vascular resistance in LAD, LCX, and collateral circulations by 35, 29, and 45%, respectively. Selective alpha 2-adrenergic blockade significantly attenuated the vasoconstrictor response to BHT.(ABSTRACT TRUNCATED AT 250 WORDS)

High-back-pressure liquid chromatography : II. Development of a post-column-controlled flow system

A liquid chromatograph including three pumps for use in micro-high-performance liquid chromatography was examined. The flow-rate of the mobile phase was controlled by a constant-flow pump located downstream of the detector. Mobile phases were supplied from two pumps, a constant-flow and a constant-pressure pump, and mixed through a T-piece. The mixing ratio could be varied stepwise by changing the flow-rate of the forward constant-flow pump. An inlet pressure required was applied in excess by the constant-pressure pump, consisting of a gas-tight syringe and a weight. This flow system permitted both stepwise gradient elution and isocratic elution. Some typical stepwise gradient separations are demonstrated.

The effects of peripheral impedance and inotropic state on the power output of the left ventricle in dogs.

The power output of the left ventricle as measured by the product of the Fourier components of aortic pressure and aortic flow is linked by definition to the arterial impedance facing the heart as measured by the quotient of these components. Consequently, the use of power measurements to assess ventricular performance can be ambiguous when accompanied by afterload changes. The heart is considered to function normally between two extremes, a constant flow pump, and a constant constant pressure pump, and two power limits are defined from these. The power limits describe the extent to which impedance changes can affect the power delivered by the left ventricle. Measured power changes that are found to lie outside the two limits can be unambiguously ascribed to changes in inotropic state. The results from preliminary dog experiments designed to test this method are reported. Cardiac sympathetic stimulation and isoprenaline infusion were used to provide a pure inotropic stimulus and a mixture of inotropic and afterload changes, respectively. The technique was able to detect inotropic changes in the heart even in the presence of simultaneous changes in afterload. Eight conventional indices of cardiac performance were monitored for comparison. The extent of their afterload dependence may not be as easily quantified.

Preparation and use of in situ chemically bonded small-particle silica as packings in high-pressure liquid chromatography

Previously we have demonstrated the feasibility of forming bonded phases on porous layer beads (Corasil II) by a completely in situ process. A logical extension of this in situ method has been its application to small-particle silica columns. Such columns have all the advantages of the bonded phases formed on porous layer beads with the added feature of much higher plate counts. In addition, when compared to commercially available small-particle bonded phase columns, the cost is reduced significantly. In this paper, both the initial column preparation procedure and the in situ technique applied to completely porous small-particle silica columns are presented. Columns were packed with a constant-pressure pump using a dibromoethane slurry procedure. After initial packing, all columns were conditioned with a solvent series of decreasing polarity and evaluated for performance using a test mixture of biphenyl ( k′ ≈ 0.5–1.0) and nitrobenzene ( k′ ≈ 5–10). After evaluation, suitable columns ( H = 0.008 ± 0.002 cm at a flow velocity of 0.55 cm/sec) were selected for in situ modification. By this procedure, differences due to variation in column packing were minimized. Subsequently, various modification procedures were investigated. As in the case of porous layer beads, control of pre-reaction surface hydration was found to be critical in determining the consistency of surfaces formed.

New ultrasonic emulsifying devices

At the Ontario Research Foundation, the Ultrasonics Applications Section has developed two alternate and novel devices for producing emulsions. This paper describes a focussing unit which concentrates longitudinal ultrasonic waves internally in a horn constructed with a parabolic end. The liquids to be emulsified, or solids to be dispersed, are passed with their carrier liquids through a channel which encloses the focus of the parabola. The other device mentioned is a modified vortex whistle, operating at a low sonic frequency of about 300Hz. A constant-pressure pump feeds the vortex whistle tangential inlet with the continuous phase (water). The disperse phase (oil) is inspirated via a specially constructed intake line, terminating in an orifice which is precisely positioned in the outlet throat of the vortex whistle. Both devices have demonstrated the capability of producing highly stable emulsions having preponderance of 1μm particles. Various paint pigments have been satisfactorily dispersed, ore slurry flotation-concentration tests have been conducted successfully and many other processes have been proved feasible, using one or other of these devices in current contract work. Patents have been applied for.

LXXIII. Variable specific-heat corrections for the efficiency of the basic internal-combustion thermodynamic cycle and their application to the Constant-volume, Constant-pressure, Diesel and Humphrey Pump cycles

Summary The following paper is offered as a contribution to the problem of facilitating variable specific-heat analysis as applied to internal-combustion motor problems in general. The approach made to these problems is new, in so far as it involves the inclusion of a fifth ratio into the analysis of the basic internal-combustion engine cycle. This ratio, besides introducing a symmetry into the resulting expressions, also enables fairly convenient expressions to be obtained for the various thermodynamic quantities such as thermal efficiency, etc.