RU2396104C1 - Device for analytical membrane filtration of fluid - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention is intended for analytical membrane filtration of fluid. Device comprises analytical membrane filter, support screen arranged in the base communicated via pipeline with evacuated filtrate collector, bottle with fluid to be filtered feeding fluid, when turned upside down, into filter, tune-holder wherein said bottle is inserted. Said bottle has its ID exceeding bottle neck OD and is jointed to the base from above. Said holder has bottle neck support representing a circular ledge with ID smaller than bottle neck OD. Pipeline is provided with valve and is connected to filtrate collector by quick-release joint.

EFFECT: possibility to replace membrane filter in sample filtration without completing filtration.

7 cl, 6 dwg, 2 tbl

Description

The invention relates to filtering devices and can be used in chemistry, microbiology, biochemistry and sanitation.

A device for analyzing contamination of biological particles of liquids, including an analytical filter, supporting its mesh, located in the base attached to the evacuated filtrate collector and a funnel for containing the filtered fluid, attached to the base from the top (Brand Catalog 1996 Laboratory Catalog Millipore p.199, USA, Millipore Corporation / PO Box 255 / Bedford, MA 01730).

Closest to the claimed technical solution is a device for analytical liquid filtration, including an analytical filter, supporting its mesh, located in the base, connected by a pipeline to the filtrate collector and a funnel for supplying the filtered liquid to the filter, an overturned bottle with filtered liquid is used as a funnel, and the device is additionally equipped with a bottle holder, attached from above to the base and representing a tube with an inner diameter exceeding d ametr used bottle neck, but less than its maximum possible depth of immersion into the tube, and 1-5 mm length greater than this depth (RU 2171128, C1). The device operates as follows. The bottle with the analyzed liquid is tipped over into the bottle holder, a portion of the liquid enters the filter, which covers the tip of the neck of the bottle, and the liquid is stopped by creating a vacuum above the liquid in the bottle. The liquid is filtered through a filter and its supporting mesh, passes through the base and enters the evacuated filtrate collector through a pipeline. When the liquid level in the holder decreases, the neck of the bottle is exposed and air enters the bottle, displacing another portion of the liquid onto the filter, which again closes the neck of the bottle, etc., until all liquid from the bottle is filtered out.

The disadvantage of this device is the inability to interrupt the filtering and change, for example, a broken or clogged filter, or filter the sample through several, for example, different porosity filters. This drawback is due to the inability to remove the neck of a bottle of liquid from a vertical holder tube without spilling liquid.

The aim of this invention is to achieve the possibility of replacing the membrane filter when filtering the sample without filtering the sample to the end.

The technical result achieved by this proposal is to achieve the possibility of changing the membrane filter when filtering the sample without filtering the sample from the bottle to the end.

The specified technical result is achieved by the fact that in the known device, including an analytical membrane filter, supporting its mesh, placed in the base, connected by a pipeline to the evacuated filtrate collector, a holder for an overturned bottle with the analyzed liquid, attached from above to the base and representing a tube with an inner diameter larger than the outer diameter of the neck of the bottle, the holder inside is equipped with a support for the neck of the bottle in the form of an annular ledge with an inner diameter of less e outer diameter of the bottle neck, and the conduit is provided with a tap and connected to a suction collection filtrate quick coupling.

Figure 1 shows the components of a device for analytical membrane filtration of a liquid and their connection with each other.

Figure 2 shows the dimensions of the neck of the bottle and the holder for it, determining its stability in this holder.

On figa, 3B shows the operation of the device.

On figa, 4B shows examples of particular cases of execution adjacent to the filter bottom of the bottle holder.

The device includes (see Fig. 1) a membrane analytical filter 1 placed on a supporting grid 2, which is located in the base 3, connected by a pipe 4, equipped with a valve 5, with a vacuum collector of the filtrate 6 using a quick disconnect connection 7a, c. On top of the analytical filter 1 is fixed in a known manner, for example, using a threaded or bayonet connection or a spring clip, the bottle holder 8, into which the bottle 9 with the filtered liquid is inserted with the neck. The bottle holder 8 is made in the form of a tube (see figure 2) with an inner diameter D _t greater than the outer diameter D _{b of the} neck of the bottle. The holder 8 is internally provided with a support 10 for the neck of the bottle 9, made in the form of an annular ledge (see figure 2) with an inner diameter D _i less than the outer diameter of the neck of the bottle D _b located at such a depth from the top of the tube H that the inner diameter of the holder D _{t is} less than the square root of the sum of the squares of the outer diameter of the bottle neck D _b and the depth H of the ledge 10.

The membrane filter 1, the supporting mesh 2, the base 3, the pipeline 4, the crane 5, the bottle holder 8 and half of the quick-connect connection 7a in the assembly form a functional unit - FG (filter head).

The device operates as follows (see figure 3).

The assembled FG filter head is put on the neck of a bottle of liquid 9 (see Fig. 3A). At the same time, the neck of the bottle 9 rests against the annular ledge 10. The bottle 9 with the liquid to be filtered together with the FG filter head is turned over and the FG filter head is connected to the filtrate collector 6 using quick disconnect connection 7a, c. (see FIG. 3B). In this case, the liquid from the bottle flows into the space above the filter 1, being replaced in the bottle with air, the pressure of which remains atmospheric until the water level above the filter reaches the edge of the neck of the bottle. After this moment, the liquid continues to flow into the space between the tube wall and the neck of the bottle, and the air pressure in the bottle above the liquid decreases, since it does not replace the leaking liquid. The process will stop when the total pressure in the plane of the edge of the neck of the bottle exerted by the column of liquid in the bottle and air above the surface of the liquid is equal to atmospheric. When the pressure in the filtrate receiver 6 decreases to p3 << p1, under the influence of this difference, the liquid begins to filter through the filter 1 and flows into the filtrate receiver 6. When the liquid level in the holder 8 reaches the edge of the neck of the bottle (or the same ring ledge), which is exposed , an air bubble will burst into the bottle and displace the corresponding portion of the liquid from the bottle, which will block the entrance to the bottle of the next portion of air until it is filtered out and the neck is exposed for the next bubble, etc. When a predetermined volume of liquid is filtered out of the bottle, the valve 5 is closed to change the filter, the quick-connect connection 7a, c is disconnected, the bottle 9 together with the FG filter head from position B (Fig. 3) is turned back to position A in Fig. 3. In this case, the liquid from the space above the filter is drained back into the bottle. But the particles deposited on the filter are not washed off from its surface, since they are held on it by the pressure difference maintained due to the presence of a valve 5, on the one hand, and on the other, as a result of the airtightness of the wetted membrane filters due to the surface tension of the liquid, and equal no less than the so-called “Bubble pressure” (T. Brock. Membrane filtration. M: Mir, 1987, p. 70, p. 83, tab. 4.1).

The filter head FG removed from the neck of the bottle 9, change the filter 1 and continue filtering.

Implement the device as follows.

The device includes (see Fig. 1) a membrane analytical filter 1 placed on a support grid 2, which is located in the base 3, connected by a pipe 4, equipped with a valve 5, with a vacuum collector of the filtrate 6 using a quick-disconnect, for example screw, bayonet, but preferably grinding conical connection 7a, c.

On top of the analytical filter 1, the bottle holder 8 is secured in a known manner, for example using a threaded or bayonet connection or a spring clip, to the bottle 9. The bottle holder 8 is made in the form of a tube (see Fig. 2) with an inner diameter D _{t is} larger than the outer diameter D _{b the} neck of the bottle.

The holder 8 is internally provided with a support 10 for the neck of the bottle 9, made in the form of an annular ledge (see figures 1, 2, 4) with an inner diameter D _i less than the outer diameter of the neck of the bottle D _b . However, in order for the liquid from the space above the filter 1 (see Fig. 3B) to pour back into the bottle 9 when the bottle with liquid 9 is flipped back, it is advisable to make the inner diameter of the step D _i smaller than the inner diameter of the neck of the bottle D ₀ (see Fig. 4B, C).

Below the upper edge of the annular ledge 10, the holder 8 is made in accordance with the diameter D _{f of the} applied filter 1, onto which it is mounted with a sealing end, which is usually made in the form of a support ring with an outer diameter approximately equal to the diameter of the filter 1, and with an inner diameter of 1- 2 mm less for pressing filter 1 to the base 3. Therefore, in the general case, some transition from the inner diameter of the annular step to the diameter of the filter working zone (which is formed when the filter is fixed between the holder tube and the base m). The inner diameter of the annular ledge can therefore increase or decrease towards the filter depending on the ratio of the diameters of the neck of the bottle and filter 1. This change can be smooth in the form of a cone, or stepwise in the form of cylinders of different diameters (see Fig. 2, 4A, 4B).

Preferably, the holder 8 of the bottle 9 provides its stability in the working inverted position without additional devices.

To this end (see FIG. 2), the depth of the support 10 from the upper edge of the tube H in combination with the outer diameter of the neck of the bottle D _b and the inner diameter D _{t of the} holder 8 (see FIG. 2) must ensure the stability of the bottle 9 in the holder 8. This condition is met if (see FIG. 2) the tube diameter Dt is less than the radius of rotation R (Dt <R) of the neck of the bottle 9 around the upper edge of the holder 8 when the bottle 9 is tipped over (for example, to the right), because under this condition, as can be seen from figure 2, the edge of the neck of the bottle will abut against the wall of the holder 8. But, as can be seen from figure 2, according to the Pythagorean theorem

,

,

hence

is a condition for the stability of the bottle 9 in the holder 8, and the maximum allowable inner diameter of the holder 8

.

.

When implementing this device, the flatness, roughness and roughness of the adjacent surfaces of the neck of the bottle 9 and ledge 10 are of importance. These parameters together should provide a sufficiently small resistance for the air flow entering the bottle 9, replacing the liquid in it. If during membrane filtration on similar devices with the placement of liquid in an open funnel, the pressure drop across the filter 1, which determines the filtration rate, is

pf = p1-p3,

where pf is the pressure drop across the filter 1, p1 is the atmospheric pressure, p3 is the residual pressure in the collector of the filtrate 6 (see Fig.3B), then when filtering using the inventive device, air resistance should be taken into account - pk when it enters the bottle 9 on the neck of the bottle 9 and the annular ledge 10

pf = (p1-p3) -pk.

From this it follows that for

pk = p1-p3

filtering will not occur.

The pressure required to overcome the surface tension of the liquid by the air bubble at the contact of the neck of the bottle 9 and the step 10 for round holes wetted by the liquid is determined (Brief Chemical Encyclopedia, ed. “Soviet Encyclopedia”, 1963, v.2, p. 411) by the formula

,

,

where p _δ = pk is the pressure necessary to overcome the surface tension of the liquid δ by the air bubble, r ₀ is the radius of the hole. Let us estimate the necessary radiuses of the holes for a special case of water, as a liquid with a large surface tension.

.

.

Typically used for vacuum membrane filtration applied vacuum approximately:

p1-p3 = 0.7 × 10 ⁵ Pa,

therefore, with such resistance on the contact, filtering will not occur.

For water

δ = 73 × 10 ^-3 N / m

then

,

,

or a diameter of 4 microns. For non-circular gaps use the concept of “reduced or equivalent diameter” (T. Brock. Membrane filtration. M: Mir, pp. 73-76). Thus, water will not be filtered on this device if the “reduced diameter” of the holes for air passage through the contact of the hydrophilic neck of the bottle 9 and the hydrophilic step 10 is less than 4 microns.

We accept for the permissible pressure loss on the mentioned contact

pk = 0.05 · 10 ⁵ Pa,

then similar to the above:

,

,

or a reduced diameter of 60 microns.

However, in practice, the real non-flatness, roughness and roughness of the contacting surfaces of the neck of the bottle 9 and the step 10 have values that together provide very small values of resistance pk, therefore, in the general case, special efforts are not required to reduce the mentioned resistance. In the event of a special case of tight abutment of surfaces, appropriate machining of the contacting surfaces of the neck and / or ledge should be applied in order to create gaps equivalent to a round diameter of at least about 60 μm. Moreover, it is preferable to create the required gaps by experimental fitting: to carry out machining in order to create the necessary gaps until the resistance at the contact of the neck of the bottle and the annular gap becomes acceptable to ensure a sufficient filtration rate through filter 1.

In the particular case of filtering aqueous solutions without surfactants, it is possible to avoid pouring water into the space bounded by the step 10, the top and inner surface of the tube 8 and the outer surface of the neck of the bottle 9 (see FIG. 3B), if the adjacent surfaces of the neck of the bottle 9 and the ledge 10 to perform hydrophobic, for example from a hydrophobic material (for example, fluoroplastic), or hydrophobize (for example, organosilicon compounds, see Brief chemical encyclopedia, ed. "Soviet Encyclopedia", 1961, v.1, p.938). Under this condition, for pushing water through hydrophobic holes with a reduced diameter of 60 μm according to the same formula above (Brief Chemical Encyclopedia, ed. “Soviet Encyclopedia”, 1963, v.2, p. 411), 0.05 × 10 ⁵ Pa is required, which corresponds to the height of the water column h = 0.5 m (see figv), which is significantly greater than the height of real bottles. But at the same time, naturally, the reduced diameter of the gaps should not exceed about 60 microns. These requirements are acceptable for a theoretical explanation, in practice, measuring and performing non-flatness, roughness and roughness, especially the determination of the equivalent diameter, are technically challenging. Therefore, it is preferable to fulfill this requirement by experimental fitting, for example, by mutually grinding adjacent surfaces to a state where water from the inverted bottle will not flow through the contact between them.

When the bottle is turned over (see FIG. 3B), first the liquid is freely poured out of the bottle, filling the space between the filter and the neck of the bottle, until its level reaches the neck, the air pressure above the liquid in the bottle does not change, since the leaked liquid is replaced by air. When the liquid level above the filter reaches the neck, air stops flowing into the space above the liquid in the bottle, and from then on, as the liquid continues to flow out, the pressure in the bottle over the liquid begins to drop until the difference in atmospheric pressure and the pressure in the bottle over the liquid is equal to the column pressure liquid in the bottle and the system will not balance.

Therefore, it is preferable that the space bounded by the outer surface of the neck of the bottle 9, the inner wall and its top of the holder 8, an annular ledge 10, has a volume sufficient to contain the liquid flowing out of the bottle during the process of establishing equilibrium when the bottle 9 is turned into the working position (see figv).

The value of the required volume is established either experimentally, by fitting, or calculated as follows.

A filter head FG is put on the neck of a bottle 9 with an inner diameter d and a total volume V ₀ , a volume of liquid V _a , a volume of air ν1 = V ₀ -V _a at atmospheric pressure p1. At the same time, the neck of the bottle 9 rests against the annular ledge 10. The bottle 9 is turned over together with the FG filter head and the FG filter head is connected to the filtrate collector 6 using quick disconnect connection 7a, c. In this case, water from the bottle flows into the space above the filter 1, being replaced in the bottle with air, the pressure of which remains atmospheric until the water level above the filter reaches the edge of the neck of the bottle. After this moment, the liquid continues to flow into the space between the tube wall and the neck of the bottle, but since air does not pass through the liquid, the air pressure p2 in the bottle above the liquid decreases. The process will stop when the total pressure in the plane of the edge of the neck of the bottle exerted by the column of liquid in the bottle ρgh (where h is the height of the liquid column from the edge of the neck to the surface of the liquid in the bottle) and the air above the liquid surface p2 is equal to atmospheric p1: p1 = ρgh + p2 . For this, the volume ν will flow from the bottle into the space between the tube wall and the neck of the bottle, and the volume of liquid V _a - ν and the volume of air ν2 at pressure p2 will remain in the bottle.

The liquid in the bottle is then held by the pressure difference above the surface of the liquid p2 and atmospheric p1

hgρ = p1-p2, or p2 = p1-hgρ

where hgρ is the pressure of the liquid column in the bottle, a h is the height of the liquid column in the bottle from the neckline to the surface of the liquid, g is the acceleration of gravity, ρ is the density of the liquid.

It's obvious that

ν1 = V ₀ -V _a ,

and ν2 = V ₀ - (V _a -ν).

From the Boyle-Marriott Act

should:

;

;

;

;

considering that hgρ << p1,

.

.

Liquid column height approx.

(см. фиг.3В);

(see FIG. 3B);

then

.

.

To filter the same liquid (ρ) from a bottle of the same diameter (d) at atmospheric pressure (p1), we form the parameter

;

;

then

;

;

whence, by opening the brackets and rearranging the variables, we define ν

;

;

;

;

.

.

Let us estimate the value of the parameter k

Taking atmospheric pressure

p1 = 0.98 · 10 ⁵ Pa;

gravity acceleration

;

;

.

.

Let us calculate, for example, the numerical values of the parameter k for medical bottles, with a volume of 125, 250, 500 and 1000 ml, with diameters of 3.5, 5, 7.5 and 11 cm, respectively, when filtering liquids with a density of 800, 1000 and 1500 kg / m ³ . The values are shown in table 1.

Table 1 The values of the parameter k (1 / m ³ ) when filtering liquids with different densities ρ from bottles of different diameters d

ρ,

d, 10 ^-2 m 800 1000 1500 3.5 87 106 162 5.0 42 52 78 7.5 19 23 35 11.0 9 10 16

,The use of bottles of more than 1 liter is inconvenient, because turning them over is already difficult. We estimate the extreme values of 1 / k in the formula:

,

.

.

Thus, this value is significantly greater than the values of V _a , V ₀ (maximum 0.001 m ³ )

Then equation (1) can be simplified

ν = V _a (V ₀ -V _a )

Now we will evaluate the practical range of values of the volume of liquid flowing out of the bottle during its revolution.

table 2 Dependence of the outflowing fluid volume ν on the volumes of the bottle V ₀ and the fluid V _a in it for liquids of different densities (through k, see table 1) V ₀ , 10 ^-6 m ³ (ml) k V _a , 10 ^-6 m ³ (ml) 25 fifty 75 one hundred 125 87 0.2 0.3 0.3 0.2 108 0.3 0.4 0.4 0.3 162 0.4 0.6 0.6 0.4 V ₀ , 10 ^-6 m ³ (ml) k V _a , 10 ^-6 m ³ (ml) fifty one hundred 150 200 250 42 0.4 0.6 0.6 0.4 52 0.5 0.8 0.8 0.5 78 0.8 1.2 1.2 0.8 V ₀ , 10 ^-6 m ³ (ml) k V _a , 10 ^-6 m ³ (ml) one hundred 200 300 400 500 19 0.8 1.1 0.8 1.1 23 0.9 1.4 1.4 0.9 35 1.4 2.1 2.1 2.1 V ₀ , 10 ^-6 m ³ (ml) k V _a , 10 ^-6 m ³ (ml) 200 400 600 800 1000 9 1.4 2.2 2.2 1.4 10 1.6 2.4 2.4 1.6 16 2.6 3.8 3.8 2.6

As can be seen from table 2, the volume of the outflowing liquid increases with increasing volume V _{0 of the} used bottle, the density of the filtered liquid, is maximum with a half-empty bottle, and for liquids with a density of 800 to 1500 kg / m ³ from 0.2 to 4 ml or relative: 0.001- 0.005 fraction of the volume V _{0 of the} applied bottle.

Obviously, the volume of the space under consideration is preferably performed at a maximum of 4 ml. This can be achieved by performing the inner diameter D _t (see FIG. 2) of the bottle holder 8, taking into account that for a given outer diameter of the neck of the bottle D _{b, the} diameter D _{t is} sufficient to form the volume under consideration. In the particular case, the required amount of space can be created by annular grooves on the inner wall of the holder above the annular ledge.

The quick disconnect connection of the FG filter head with the filtrate receiver 6 is preferably performed using a tapered connection 7a, b, because this connection is faster than bayonet or screw (requiring two-handed manipulation), and simpler - no manipulation is required (just insert or remove).

As specific examples of the implementation of the inventive device in figure 2 shows the following:

D _f = 35 mm, D _i = 32 mm, D _t = 34 mm, D _b = 33 mm, D ₀ = 25 mm,

H = 21 mm (see figure 2),

применяемых медицинских склянок: 125/3.5, 250/5.0, 500/7.5, 1000/11 (фиг.3).volume, ml / diameter, cm

applicable medical bottles: 125 / 3.5, 250 / 5.0, 500 / 7.5, 1000/11 (figure 3).

And in Fig. 4: D _i = 22 mm, D _f = 47 mm (Fig. 4A); D _i = 23 mm, D _f = 25 mm (Fig. 4B); the remaining sizes are as previously indicated for figure 2.

Thus, the claimed distinctive features provide in the aggregate the achievement of the claimed technical result, consisting in achieving the possibility of changing the filter without filtering the sample from the bottle to the end, as follows.

The fact that the holder inside is equipped with a support for the neck of the bottle in the form of an annular ledge with an inner diameter smaller than the outer diameter of the neck of the bottle, provides the possibility of overturning the bottle with the filter head without spilling some liquid in the space above the filter when filtering is interrupted. the adjoining edge of the neck of the bottle to the surface of the ledge creates a sufficiently reliable channel for the flow of this volume back into the bottle. In addition, the presence of an annular ledge allows you to stably position the neck of the bottle relative to the filter. The diameters of the filters used can be different: more or less than the diameter of the neck of the bottle. Therefore, in the general case, some transition from the inner diameter of the annular step to the diameter of the filter working zone (which is formed when the filter is fixed between the holder tube and the base) is necessary. The inner diameter of the annular step can therefore expand or decrease towards the filter depending on the ratio of the diameters of the neck of the bottle and the filter. This change can be smooth in the form of a cone, or stepwise - in the form of cylinders of different diameters.

The presence of a quick-disconnect connection makes it possible to disconnect the filter head from the filtrate receiver, put it on the neck of the bottle with the filtered liquid, tilt the bottle together with the filter head and attach the latter to the filtrate receiver without the risk of liquid spill.

Closing the tap on the pipeline ensures the preservation of the pressure drop across the filter, which keeps the particles deposited on the filter from being washed off when the bottle is tilted back from its working position.

These signs are necessary to achieve a technical result.

Additional features provide additional benefits when implementing the device.

The location of the annular ledge at such a depth from the top of the holder that the inner diameter of the holder is less than the square root of the sum of the squares of the outer diameter of the neck of the bottle and the depth of the location of the ledge ensures that the bottle is positioned in the holder at a predetermined distance from the filter and ensures its stability against tipping over working position.

The inner diameter of the annular ledge, made smaller than the inner diameter of the neck of the used bottle, when the bottle with liquid is flipped back allows the latter to flow more reliably from the space above the filter back into the bottle.

The sufficiency of the volume of space bounded by the surface of the ledge, the inner surface and the upper edge of the tube and the outer surface of the neck of the bottle prevents leakage of part of the liquid through the upper edge of the tube during the flipping of the bottle to its working position.

The quick connection of the filter head with the filtrate receiver in the form of a polished conical connection provides the convenience and speed of attaching the filter head to the filtrate receiver with one hand.

Claims (7)

1. Device for analytical membrane filtration of a liquid, including an analytical membrane filter, supporting its mesh, located at the base, connected by a pipeline to a vacuum collector of the filtrate, a bottle with filtered liquid used in the capsized state to supply liquid to the filter, the holder tube into which an inverted bottle with a liquid is inserted having an inner diameter larger than the outer diameter of the neck of the bottle and attached from above to the base, characterized in that it holds The inside is equipped with a support for the neck of the bottle in the form of an annular ledge with an inner diameter smaller than the outer diameter of the neck of the bottle, the pipeline is equipped with a tap and is connected to the filtrate receiver by a quick-disconnect connection. 2. The device according to claim 1, characterized in that the annular ledge is located at such a depth from the top of the holder that the inner diameter of the holder is less than the square root of the sum of the squares of the outer diameter of the neck of the bottle and the depth of the ledge. 3. The device according to claim 1, characterized in that the inner diameter of the annular ledge is less than the inner diameter of the neck of the bottle used. 4. The device according to claim 1, characterized in that the inner diameter of the annular step increases or decreases in the direction of the filter to a diameter less than the diameter of the filter by an amount necessary to seal the edges of the filter between the end face of the holder and the base. 5. The device according to claim 1, characterized in that the amount of space between the ledge, the lateral outer surface of the neck of the bottle, the inner surface and the top of the holder tube is sufficient to accommodate the liquid flowing out of the bottle at the time of its revolution in the working position, and is more than 0.001 -0.005 volume of the used bottle depending on its volume, internal diameter and density of the filtered liquid. 6. The device according to claim 1, characterized in that the quick disconnect connection is a conical grinding. 7. The device according to any one of claims 1 to 4 and 6 for a special case of aqueous solutions, characterized in that the adjacent surfaces of the neck of the bottle and the annular ledge are made hydrophobic, moreover, the roughness, flatness and roughness of these surfaces together provide a sufficient gap between them, sufficient to hold a pillar of water the height of a bottle.

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