Hydraulic Locking In Spool-Type Valves. Tapered Clearances Analysis

The paper deals with the analysis on the influence of geometrical characteristics on the locking force acting on spools in tapered clearances exposed to decentralizing pressure drops. An estimation is presented of the different results in locking force prediction deriving from the comparison of the "classical" one-dimensional approach of flow and a more complex description represented by the Reynolds equation. A sensitivity analysis on the influence of clearance geometrical parameters is performed, showing the limits of application of the one-dimensional approach. Two non-dimensional geometric variables are identified, which can be adopted to define some polynomial corrective functions correlating one-dimensional results with more reliable two-dimensional solutions. The determination of the locking force can therefore be performed by an analytical process, involving the "classical" one-dimensional solution and a polynomial correction which is a simple two-variable function of the clearance geometry. In comparison with results coming from the direct solution of the Reynolds equation, the process leads to errors confined within the range of a few per cent, considering clearances in a wide dimensional range representing a large amount of couplings actually encountered in hydraulic spool valves

Possible bradycardic mode of death and successful pacemaker treatment in a large family with features of long QT syndrome type 3 and Brugada syndrome

We recently identified a novel mutation of SCN5A (1795insD) in a large family with features of both long QT syndrome type 3 and the Brugada syndrome. The purpose of this study was to detail the clinical features and efficacy of pacemaker therapy in preventing sudden death in this family. The study group consisted of 116 adult family members: 60 carriers (29 males) and 56 noncarriers (28 males) of the mutant gene. Investigations included 24-hour Holter monitoring, ergometry, and electrophysiologic studies. Mean, lowest, and highest heart rate were lower in the carriers, but heart rate variability was comparable. In carriers, disproportional QT prolongation was present during bradycardia. No complex ventricular ectopy was recorded, and there were fewer isolated premature beats (both ventricular and atrial) in carriers. All patients were asymptomatic, except for two individuals who experienced syncope; in one of these patients, asystolic episodes (up to 9 sec) were repeatedly recorded. Prolonged HV intervals were present in 5 of 6 patients. Thirty carriers received a prophylactic backup pacemaker. During median follow-up of 4.5 years (range 0.0 to 22.6), their survival rate was 100%. There were five sudden deaths among the remaining 30 carriers without a pacemaker (P = 0.019). This family with a high incidence of nocturnal sudden death is characterized by bradycardia-dependent QT prolongation, intrinsic sinus node dysfunction, and generalized conduction abnormalities. There is a striking absence of complex ventricular ectopy, and pacemaker implantation was effective in preventing sudden death. These findings raise the possibility of a bradycardic rather than tachycardic mode of deat