Procedure and device for the leak testing of porous pipes.

The invention relates to a method for testing of pipes or the like made of concrete, stoneware, cast iron or the like for leaks using a Vakuumprüf device....; An apparatus for performing the method, wherein the test specimen is sealed on both sides, one of said seals is provided with a connection to a vacuum pump, and wherein means are provided for measuring the negative pressure.

The invention is based on the known test methods for pipes made of stoneware, clay, concrete or similar porous materials in which both pipe ends are closed with gasketed test plates, one of which has a connecting piece for a vacuum unit, with the aid of the tube, a vacuum is produced. The decrease of the vacuum, or the resulting under the effect of the negative pressure from the outside penetrating in irrigation water Feuchstellen inside, allow at least the evaluation of the test specimen for leaks or their quantitative determination. Further, it is known to examine such pipes under excess pressure and to determine a drop of the excess pressure over time. However, the application of this method leads to uncertain results, because especially in the clock-production can not be delayed sufficiently long, as would be necessary for setting a steady-state equilibrium. The setting of the steady-state equilibrium is delayed in particular by the power consumed for the adiabatic expansion of the air when pulling the vacuum thermal energy. Another delay occurs due to the evaporation of still contained in pore residual water, which cause a cooling of the (residual) air content in the specimen and thus a lowering of the pressure, causing a leak can be simulated, which is not given.

This is where the invention which underlies the object to provide a generic method that adjusting the stationary equilibrium speeds and clock manufacturing causes a shortening of the examination time; Further it is an object of the invention to provide a for performing the method suitable, generic device with which the vacuum test can be performed safely and undisturbed even with short cycle times.

According to the invention, this object is achieved as regards the procedure in the main claim 1, and with regard to the device by the features specified in the claim 4 features; Advantageous developments and preferred embodiments of the method described in the dependent claims 2 and 3 and advantageous developments and preferred embodiments of the apparatus are described in the dependent Claims 5 to 10th

Pulling a vacuum in the test specimen on both sides sealed by means of a connected vacuum pump, a statement about the tightness of the test object can be made from the loss of vacuum after switching off the suction. This statement is, however insecure if changed, the internal pressure in the test piece after stopping the suction caused by temperature changes. It can therefore be carried out for a meaningful measurement only when a steady state is reached in terms of temperature. To bring about this condition faster, still present in the test specimen residual air is circulated by means of a fan during evacuation, wherein the fan is preferably driven electrically. Each fan has a contingent of its design efficiency, indicating which portion of the supplied energy is converted into mechanical work for conveying the air and how much of the power dissipation directly into heat, which also applied in conveying the air flow in a closed system ultimately merges into heat. This phenomenon may explain why through the circulation of the residual air contributes to accelerate the adjustment necessary for testing stationary equilibrium. Alternatively, in the tube to be tested, the test specimen, heat energy released, the amount of heat released at least equal to that used during adiabatic expansion of air when pulling the vacuum heat. Here is a direct thermal influence is present in the setting of the stationary equilibrium, the acceleration of setting can be explained in the same way. This introduced into the system heat temperature reduction is counteracted during the pulling of the vacuum and it is a priori a necessary precondition that the stationary equilibrium is established with sufficient speed so that the lead time for the actual measurement can be shortened. If by an inadmissible loss of vacuum, or too rapid a rise in the pressure in the specimen, during subsequent to the lead-time measurement time determined leakage, the candidate is deemed leak and -ggf. singled out a Nachbehandlung-.

Particularly advantageous when the porous test samples, in the pores of significant amounts of water can be stored, if the liberated in the test piece heat quantity also comprises the amount of heat corresponding to the heat of vaporization of the water, which evaporates during drawing of the vacuum and thereafter. Residual water on the surface or in (surface-near) pores of the test specimen is in pulling the vacuum and even later evaporated, leaving substantial amounts of heat are consumed as heat of vaporization. These so consumed heat is extracted from the material of the test object, which thus cools, so that once again continue to flow in the resulting temperature drop of the residual air in the test sample quantities of heat in the material, which leads to a cooling of the residual air, so that a volume reduction and thus a pressure drop the consequences are. By this cooling, which is connected in dense specimen with a reduction of the pressure, is caused pressure increase at least delayed when leaking pipe of flowing through the leakage air and thus a tightness of the DUT feigned that need not be given. This phenomenon affects the supply of additional heat counter in turn, so that even when wet surfaces or materials the vacuum test can be carried out undisturbed.

To perform the test, the test piece is on both sides sealed, one of said seals is provided with a connection to a vacuum pump, and wherein means are provided for measuring the negative pressure, it is advantageous if in the test specimen an operated from outside the fan and / or operated from the outside heat source is / are arranged. The fan advantageously has an electric drive on, the switched from the outside, possibly can also be provided with regard to the fan speed; with the rotational speed of the fan can be brought to a desired value the power consumed by him electric power, with the switchability of the fan can also be clocked so that the introduced into the system of energy independent of the power consumed by drive power by the pulse ratio on the desired value can be set. The heat source advantageously comprises an electric heater with the heat source can be switched and provided also in terms of power output, so that the system power supplied also brought to the desired value and its heat output can be limited. In an advantageous embodiment, the electric heat source is provided with means for regulating its temperature, which allows the regulation of the votes from the heat source heat quantity.

The distribution of the votes from the heat source in the interior of the test piece heat this is advantageously connected to a blower. In large-volume-test items, it is necessary and advantageous if the heat emitted from the heat source in the specimen is distributed with fluidic means in the specimen. For this purpose, the fan, which can be combined with the heat source to an installation unit, such as a fan heater suitable. This heat source is advantageously attached directly to at least one of the sealing of the specimen causing endplate; An alternative arrangement is provided in that the heat source is fixed to an intermediate ring which is secured at least between one of the sealed ends of the specimen and the test specimen of the sealing end plate corresponding seals. With this arrangement, bear the heat source for both the end plate and an intermediate ring, it being understood of course that also the intermediate ring to the terminal may be provided for the vacuum pump.

In a preferred embodiment a fan is provided as a heat source, which is provided with a Heizelelement. With the fan of the heat source by releasing heat amounts heated air can also be distributed in large-volume test items so that the stationary equilibrium is established quickly and the lead time lying by the test time can be kept short. The air flow caused by the fan is rich mixture turbulence, thus ensuring the desired mixing with the present in the cavity of the device under test (residual) air.

In another embodiment, one into the lumen of the test piece insertable with play displacer is provided, which forms the heat source and which is provided for this purpose with heating means for keeping the surface temperature. By introducing this displacement body which is to be evacuated air volume is reduced, leading to a reduced time for pulling the vacuum. On the other hand also which is under the influence of the temperature reduction volume of the (residual) air in the test piece is reduced, which promotes the temperature compensation, because the surface of the displacement body is held at a constant surface temperature. The free annular gap in the specimen can be held so as to face the free path of the gas molecules of the (residual) air is large, so that heat conduction and heat transfer are not hindered (at a vacuum of 99%, corresponding to a pressure (absolute) 0.01 bar this is still below 10⁻³m). Finally, in this embodiment, the radiant heat to compensate the heat loss through the evaporating from the surface of the sample amount of water, in which case the surface temperature is maintained at a predetermined height.

It is advantageous as heating means for keeping the surface temperature of a filling provided with a liquid heating medium, which with a heater the necessary for keeping the surface temperature of heat can be supplied. This filling with a liquid heat transfer medium is ensured that the released by the heating amount of heat is distributed throughout the volume, including convection suffice. If according to an advantageous embodiment, the heating device located outside the Wäremquelle, allows the liquid heat transfer heat transfer via a circuit, the circuit flow contributes to the formation of the desired convection in the test piece. If, after another development, the heater positioned within the heat source, means are advantageously provided which circulate the liquid heat exchanger inside the heat source so that a forced convection is achieved here too.

For monitoring and also for regulation of the output quantities of heat, the heat source is provided with at least one temperature sensor with which the temperature of the exchanger surface with the (residual) air in the test piece co-operating surface of the heat source is removed. At the same time, or alternatively, the heat source is provided with at least one temperature sensor, to decrease the temperature of the liquid heat transfer medium or the heating core, in particular the temperature of the heat-generating electric heating coil. This monitoring can be the temperature control so that the tightness determination affecting heat loss can be compensated for, which must first be made to empirically determined relationships. For this, the temperature sensor has an advantageous together with a control loop which keeps the temperature on the amount of heat given to the desired size. A predictive control is achieved when monitoring a computer, such as a personal computer, is used which calculates the heat demand based on a thermal model and heat output controls accordingly.

The essence of the invention is explained in detail using the embodiments shown in Figures 1 and 2; show case<dl id="dl0001"><dt>Figure 01.:</dt><dd>A section of a sample having arranged inside the heat source in the form of a fan heater;</dd><dt>Figure 02.:</dt><dd>DUT with arranged inside displacement body with a heat source with liquid heat carrier.</dd></dl>

Figures 1 and 2 show the device under test 1, a partial cut concrete pipe which is clamped for testing the tightness between the end plates 2 and 3. FIG. It goes without saying that these end plates 2 and 3 parts of a (not shown) test stand, the test stand can also be adapted to a cyclically examination of the specimens 1 done that in on a transport device lying by the inspection station the course of the production test stand designed to be transported. Via the connection line 4, the end plate 3 is connected to a suction pump, which evacuates the inside of the test object 1 to the desired or required test pressure. After reaching the desired or required vacuum, the gate valve 5 is closed, so that the compound of Sample 1 is interrupted to the suction pump. Leaks in the wall of the test specimen can now flow in air, so that the vacuum is degraded, with the result that the pressure in the interior of the test specimen increases. A pressure switch 6 allows to track this change in pressure, possibly also with remote transmission to a control center, where the result is also printed out. This pressure monitoring for testing assumes that the change in pressure inside the test object is solely due to leaks. If pressure changes simulated by temperature changes, given the tightness test uncertainty, the main cause of this uncertainty is to be sought in a lowering of the temperature inside the test piece 1, eg by adiabatic expansion of the air when pulling the vacuum or by the extraction of heat due to the heat of vaporization of from the wall of the still-moist concrete evaporating water. This temperature reduction a pressure-lowering is effected, which can be counteracted by the addition of heat.

1 shows a simple way to supply the heat energy; Here, a holding frame 7 is attached to the one end plate 3 is arranged, preferably eccentrically, which is provided with a fan heater eighth The heater includes a fan 8 8.1, which circulates the one (not shown in detail) electrical heating element heated air, said blower and heating element 8.1 are electrically connected via the connection line 8.2. The air in the interior of the specimen is sucked by the fan of the heater 8 and 8.1 recycled as a free jet through the nozzle 9 into the interior of the test object first In this cycle, the heat emitted by the heating element is fed, despite adiabatic expansion and despite withdrawal of heat by evaporating water does not leave the air temperature drop. It seems obvious that at least the heating element of the heater 8 can be used regulated; Also the temperature of the discharged air by means of a (not shown) temperature sensor is appropriately monitored so that a lowering is indeed prevented, a measurable rise in temperature of the air inside the test piece, however, does not occur.

2 shows an alternative solution in which, for a volume of the inner space is reduced and is introduced to another heat by heated surfaces. Here the Entplatte 3 is provided with an insertable into the interior of the specimen 1 displacer 10, the diameter of which is well below the diameter of the specimen. Because of this substantially coaxially arranged displacement body 10 here is the suction port 4 installed in the area of ​​the plug sleeve 1.1 of the test piece 1, so that can be freely sucked. The displacement body 10 is provided with a heater, through its surface can be maintained at a temperature such that can be supplemented by adiabatic expansion or by evaporation of water consumed heat energy. Given in the displacer 10, a heater is provided which is connected by means of supply and return 11 to a heat supply. In the illustration of Figure 2 the other end plate 2 is provided with an analog displacement body, which is carried out heating of an electrically operated heating element, which is connected via the connecting line 12 to an electrical supply. The length of the displacement body 10 can -to the length of the displacement body 10 and the path length limit for withdrawing the end plate 3, are kept shorter than the length of the sample 1; another possibility is given by the fact that the displacement body 10 is also divided such that the end plate 3 is provided with respect to the length of the sample 1 shorter displacement body 10, and the other test plate 2 with a displacement body 10 ', held its length so is that the sum of the lengths of the two displacement bodies 10 and 10 'is shorter than the length of the specimen.