Sludge treatment medicament screening device

Abstract

The invention relates to the technical field of sludge reduction, in particular to a sludge treatment agent screening device. The device comprises a batching system, a reaction system and a cleaning system, the batching system comprises a transmission mechanism, and only one transmission motor is arranged in the transmission mechanism, so that the direct transmission of the sludge container and the selective transmission of the medicament container can be realized, the use is convenient, and the equipment cost is saved; the reaction containers in the reaction system and the cleaning system can be mutually switched, the cleaned reaction containers can be used for reaction, the reacted reaction containers can be used for cleaning, a stirring paddle and a cleaning brush are prevented from being disassembled and assembled while switching is achieved through the lifting switching mechanism, use is more convenient, and improvement of the experiment efficiency is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of sludge reduction, and in particular to a sludge treatment and disposal agent screening device. Background Art

[0002] Activated sludge is a general term for microbial communities and the organic and inorganic substances they are attached to. A large amount of residual sludge will be produced in the process of biological sewage treatment. Since the residual sludge contains a large amount of organic matter, it is a recyclable resource. However, if it is not treated in time and randomly piled up, pollutants such as nitrogen, phosphorus, heavy metals and harmful chemicals will seep out, polluting the land, rivers, lakes and groundwater, and causing harm to the environment.

[0003] The treatment and disposal of activated sludge is particularly important. Since the water content of activated sludge is high, reaching more than 98%, the necessary reduction in the process of treatment and disposal is crucial. In the process of sludge reduction, the sludge needs to be conditioned. The conditioning agent used is directly related to the dewatering performance of the sludge, which is of great significance to the sludge dewatering effect and cost reduction and efficiency improvement. The existing sludge dewatering device is often equipped with a stirring motor for each agent device during use, which increases the cost of the equipment. On the other hand, the reaction vessel needs to be cleaned after an experiment is completed, which is not conducive to improving the efficiency of the experiment.

[0004] Therefore, the present invention proposes a drug screening device for sludge treatment and disposal. The device of the present invention is used to screen the drugs in the sludge treatment process. On the one hand, the manufacturing cost of the device is low, and on the other hand, it is convenient for cleaning and replacement of the reaction container. At the same time, multiple groups of reactions can be carried out simultaneously, which is convenient for use and is also conducive to improving the screening efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a sludge treatment and disposal agent screening device to solve the problem that the existing sludge dewatering equipment uses multiple motors, has high manufacturing costs, and requires time to clean after use, thus affecting the experimental efficiency.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a sludge treatment and disposal agent screening device, including a batching system, a reaction system and a cleaning system;

[0007] The batching system includes a transmission mechanism, a sludge container and a reagent container. The transmission mechanism directly drives the stirring paddle in the sludge container, and the transmission mechanism can selectively drive the stirring paddle in the reagent container through a matching mechanism; the liquid in the sludge container and the reagent container is transported to the reaction system;

[0008] The reaction system comprises a reaction container, and the liquid in the sludge container and the reagent container is transported to the reaction container, a stirring paddle is arranged in the reaction container, and a suction filter device is arranged below the reaction container, and the suction filter device is connected to a vacuum pump;

[0009] The cleaning system comprises a reaction container, a cleaning brush is arranged in the reaction container, a beaker container is arranged below the reaction container, and the beaker container cooperates with a sewage tank; a cleaning pipe is arranged at the bottom of the reagent container, a control valve is arranged on the cleaning pipe, and the cleaning pipe cooperates with the sewage tank;

[0010] The reaction container in the reaction system and the reaction container in the cleaning system are switched with each other through a lifting conversion mechanism.

[0011] Furthermore, the transmission mechanism includes a transmission motor, which is connected to a transmission gear and is provided with a driven gear, and the transmission gear is transmission-connected to the driven gear through a transmission chain; the transmission chain is simultaneously transmission-connected to multiple first mating gears, and each first mating gear is matched with a second mating gear; one of the second mating gears is directly transmission-connected to a stirring paddle in the sludge container; and the remaining second mating gears are transmission-connected to a stirring paddle in the reagent container through a mating mechanism.

[0012] Furthermore, the mating mechanism includes two transmission parts arranged up and down, which are a first transmission part and a second transmission part respectively. The first transmission part is located below the second mating gear and is transmission-connected to the second mating gear, and a first telescopic support mechanism is supported and arranged below the first transmission part; and a mating part is provided, the second transmission part is located above the mating part and is transmission-connected to the mating part, and a second telescopic support mechanism is supported and arranged above the second transmission part; the mating part and the second mating gear are fixedly connected to the rotating shaft, and the rotating shaft is transmission-connected to the stirring paddle; when the second telescopic support mechanism is extended, the first telescopic support mechanism is compressed, and the transmission between the first mating gear and the second mating gear is disconnected; when the second telescopic mechanism is contracted, the first telescopic support mechanism is restored, and the first mating gear and the second mating gear resume transmission.

[0013] Furthermore, the transmission member includes a first part and a second part, and through holes are provided at the center of the first part and the second part, and the through holes cooperate with the rotating shaft; a placement groove is provided on the first part, and a ball is placed in the placement groove; the second part is detachably fixedly connected to the first part, and a groove is provided around the second part, and the groove cooperates with the placement groove. When the second part is fixed on the first part, the diameter of the groove is smaller than the diameter of the ball.

[0014] Furthermore, the first telescopic support mechanism includes a spring, a telescopic rod is arranged outside the spring, the telescopic rod includes an outer tube and an inner tube, and the outer tube is sleeved on the inner tube.

[0015] Furthermore, the second telescopic support mechanism includes an annular air chamber, a piston connecting part is arranged around the annular air chamber, a piston is arranged in the piston connecting part, and a piston rod of the piston is fixedly connected to the second transmission member; one side of the annular air chamber is connected to the inflation ball through an air pipe, and an exhaust valve is arranged on the air pipe.

[0016] Furthermore, the lifting conversion mechanism includes a mechanism box, the mechanism box is connected to the connecting rod, and the connecting rod is respectively connected to the reaction container in the reaction system and the reaction container in the cleaning system.

[0017] Furthermore, the mechanism box includes an upper part and a lower part, a worm wheel is arranged in the upper part, the worm wheel cooperates with the worm, and the worm is connected to the handwheel outside the upper part; the worm wheel is threadedly connected to the lead screw through a thread at the center, the upper end of the lead screw is connected to the connecting rod, the lower end of the lead screw extends to the lower part, a limiting hole is arranged at the lower end of the lead screw, a strip groove is arranged on the outer side wall of the lower part, a limiting pin is inserted in the strip groove, and the limiting pin cooperates with the limiting hole.

[0018] Beneficial effects of the present invention:

[0019] 1. The present invention uses one motor to stir the sludge container and the reagent container, which can effectively reduce the manufacturing cost. When the sleeve is used, the stirring paddle in the reagent container can be selectively opened and closed, which is more convenient to use;

[0020] 2. The present invention separates the reaction from the cleaning phase and switches them through a lifting conversion mechanism. The cleaning does not affect the continuation of the reaction, which is beneficial to improving the experimental efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the device of the present invention;

[0022] Figure 2 It is a schematic diagram of the structure above the third support plate of the present invention;

[0023] Figure 3 It is a schematic diagram of the transmission mechanism structure in the mechanism box of the present invention;

[0024] Figure 4 The present invention Figure 2 A partial enlarged schematic diagram of part A;

[0025] Figure 5 It is a schematic diagram of the transmission structure of the present invention;

[0026] Figure 6 is a schematic structural diagram of a second telescopic support mechanism of the present invention;

[0027] Figure 7It is a schematic diagram of the installation arrangement of the delivery pump of the present invention;

[0028] Figure 8 It is a schematic diagram of the structure above the first support plate and the second support plate of the present invention;

[0029] Fig. 9 It is a schematic diagram of the top view of the support frame of the present invention;

[0030] Fig.10 The present invention Figure 7 A partial enlarged schematic diagram of part B;

[0031] Fig.11 It is a schematic diagram of the internal structure of the regulating conversion mechanism of the present invention;

[0032] Fig.12 It is a schematic diagram of the cooperation between the worm gear and the lead screw of the present invention.

[0033] The names corresponding to the marks in the figure are:

[0034] 1. Screening device; 11. Bottom plate; 111. Universal wheel; 12. Side plate; 13. First support plate; 14. Second support plate; 141. Support frame; 1411. Stirring paddle matching hole; 1412. Feed matching hole; 15. Third support plate; 151. Sludge container; 152. First medicine container; 153. Second medicine container; 154. Third medicine container; 155. Fourth medicine container; 156. Delivery pump; 157. Cleaning pipeline; 1571. Control valve; 158. Stirring motor; 1581. First stirring paddle; 159. Cleaning motor; 1591. Cleaning brush; 16. Mechanism box; 161. Transmission mechanism; 1611. Transmission motor; 1612. Transmission gear; 1613. Driven gear; 1614 , transmission chain; 1615, first matching gear; 1616, second matching gear; 162, matching mechanism; 1621, top groove; 1622, rotating shaft; 1623, first transmission member; 1624, first telescopic support mechanism; 1625, shell; 1626, matching member; 1627, second transmission member; 1628, second telescopic support mechanism; 163, second stirring paddle; 17, lifting conversion mechanism; 171, mechanism box; 1711, strip groove; 1712, limit pin; 1713, hand wheel; 1714, lead screw; 1715, worm wheel; 1716, worm; 1717, limit hole; 172, connecting rod; 173, reaction vessel; 2, vacuum pump; 3, sewage tank; 4, filtration device; 5, beaker. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0036] like Figure 1-7As shown, the screening device 1 of the present invention includes a bottom plate 11, side plates 12 are arranged on both sides of the bottom plate 11, and a first support plate 13, a second support plate 14, a third support plate 15 and a mechanism box 16 are arranged in sequence from bottom to top through the side plates 12; a universal wheel 111 is installed below the bottom plate 11, and a vacuum pump 2 and a sewage tank 3 are placed on the first support plate 13.

[0037] A sludge container 151 is arranged above the third support plate 15, and multiple chemical containers are arranged, namely a first chemical container 152, a second chemical container 153, a third chemical container 154 and a fourth chemical container 155; a transmission mechanism 161 is arranged in the installation box, and the transmission mechanism 161 simultaneously transmits the second stirring paddles 163 in the multiple chemical containers through the matching mechanism 162; the transmission mechanism 161 directly transmits the second stirring paddle 163 in the sludge container 151.

[0038] The transmission mechanism 161 includes a transmission motor 1611, which is located above the mechanism box 16. The transmission motor 1611 is connected to a transmission gear 1612 in the mechanism box 16. A driven gear 1613 is also provided in the mechanism box 16. The transmission gear 1612 cooperates with the driven gear 1613 through a transmission chain 1614, and cooperates with five first matching gears 1615 through the transmission chain 1614 at the same time. Each first matching gear 1615 is meshed with a second matching gear 1616 for transmission; one of the second matching gears 1616 does not cooperate with the matching mechanism 162, and its rotating shaft 1622 is directly connected to the lower side of the mechanism box 16, and the lower side of the rotating shaft 1622 is connected to the second stirring paddle 163 in the sludge container 151 through a copper chuck; the other four second matching gears 1616 cooperate with the matching mechanism 162, and are connected to the second stirring paddles 163 in the four medicine containers through the matching mechanism 162.

[0039] The matching mechanism 162 is provided with a first transmission member 1623 in the mechanism box 16. The first transmission member 1623 is located below the second matching gear 1616 (a groove is provided below the second matching gear 1616) and is in rolling contact with the second matching gear 1616. The first transmission member 1623 includes a first part and a second part. Through holes are provided at the centers of the first part and the second part, and the through holes are matched with the rotating shaft 1622. A placement groove is provided on the first part, and a ball is placed in the placement groove. The second part is detachably fixedly connected to the first part, and the second part is detachably fixedly connected to the first part. A groove is arranged around the periphery, which cooperates with the placement groove. When the second part is fixed on the first part, the diameter of the groove is smaller than the diameter of the ball to prevent the ball from falling out of the groove; a first telescopic support mechanism 1624 is arranged between the lower side of the first transmission member 1623 and the inner lower side of the mechanism box 16, and the first telescopic mechanism includes a spring, and a telescopic rod is arranged outside the spring. The telescopic rod includes an inner tube and an outer tube, and the outer tube is sleeved on the inner tube. When the outer tube contacts the inner lower side of the mechanism box 16, the second matching gear 1616 and the first matching gear 1615 disconnect the transmission.

[0040] The matching mechanism 162 is provided with a shell 1625 below the mechanism box 16, and a matching piece 1626 is provided in the shell 1625. The matching piece 1626 is fixedly connected to the rotating shaft 1622 and matched with the second transmission piece 1627 above the matching piece 1626. A groove is provided above the matching piece 1626. The structure of the second transmission piece 1627 is consistent with the first transmission piece 1623. A second telescopic support mechanism 1628 is provided between the second transmission piece 1627 and the lower bottom surface of the mechanism box 16. The second telescopic mechanism includes an annular air chamber, and a piston connecting part is provided around the annular air chamber. The piston connecting part is provided with four and evenly distributed parts. A piston is provided in the piston connecting part. The piston is connected to a piston rod, and the piston rod is fixedly connected to the top of the second connecting part; the annular air chamber is connected to the inflation ball through an air pipe, and a one-way air valve for intake of air into the air pipe is provided at the connection between the inflation ball and the air pipe, and a valve for intake of air from the outside into the inflation ball is provided on the other side of the inflation ball. A one-way air valve for air is provided on the air pipe; air is inflated into the annular air chamber through the inflation ball, at which time the piston moves downward and pushes the second transmission member 1627, and the second transmission member 1627 pushes the matching member 1626 downward so that the rotating shaft 1622 moves downward as a whole, the spring in the first telescopic support mechanism 1624 is compressed, the corresponding second matching gear 1616 moves downward, the transmission connection between the second matching gear 1616 and the corresponding first matching gear 1615 is disconnected, and the corresponding second stirring paddle 163 in the medicine container does not work; when the gas in the annular air chamber is released through the exhaust valve, the spring in the first telescopic support mechanism 1624 pushes the first transmission member 1623 to move upward, and drives the corresponding second matching gear 1616 to move upward, the second matching gear 1616 is meshed with the corresponding first matching gear 1615 to realize the transmission process, at which time the upper end of the rotating shaft 1622 is matched with the top groove 1621 on the top side of the inner top of the mechanism box 16.

[0041] A delivery pump 156 is arranged corresponding to each container on the third support plate 15, and the delivery pump 156 is a peristaltic pump. A cleaning pipe 157 is also arranged at the bottom of each container, and a control valve 1571 is arranged on each cleaning pipe 157. The cleaning pipes 157 are connected to the sewage tank 3 on the bottom plate 11 after being collected.

[0042] like Figure 1 , 8-12, a stirring motor 158 and a cleaning motor 159 are arranged below the second support plate 14, the stirring motor 158 is connected to the first stirring paddle 1581, and the cleaning motor 159 is connected to the cleaning brush 1591. An opening is arranged on the second support plate 14, and the reaction container 173 is arranged in the opening. A support frame 141 is arranged above the opening in the reaction zone, and the support frame 141 includes a stirring paddle matching hole 1411 and a feed matching hole 1412 located in the middle. The stirring paddle matching hole 1411 matches with the first stirring paddle 1581, and the feed matching hole 1412 matches with the sludge container 151 and the delivery pipes of each reagent container delivery pump 156 respectively.

[0043] Multiple reaction containers 173 can be set, such as one backup and one use, two backup and two use, and three backup and three use, etc. A valve is set at the bottom of the reaction container 173; a suction filtration device 4 is placed below the reaction container 173 in the reaction area, and the suction filtration device 4 is matched with a vacuum pump 2 (constant pressure); a beaker 5 container containing cleaning liquid is set below the reaction container 173 in the cleaning area, and the waste liquid in the beaker 5 container is collected in the sewage tank 3; the bottom of each reaction container 173 is connected to the lifting conversion mechanism 17 through a connecting rod 172.

[0044] The lifting conversion mechanism 17 includes a mechanism box 171, which includes an upper part and a lower part. A worm wheel 1715 is provided in the upper part (the worm wheel 1715 can rotate freely, but the upper and lower spatial positions remain unchanged). The worm wheel 1715 cooperates with a worm 1716, and the worm 1716 is connected to a hand wheel 1713 outside the upper part; the worm wheel 1715 is threadedly connected to a lead screw 1714 at the center of the worm wheel 1715. The lead screw 1714 is threadedly connected to the lead screw 1714. The upper end of the lead screw 1714 is connected to the connecting rod 172, and the lower end of the lead screw 1714 extends to the lower half. A limit hole 1717 is provided at the lower end of the lead screw 1714, and a strip groove 1711 is provided on the outside of the lower half. A limit pin 1712 is inserted in the strip groove 1711, and the limit pin 1712 cooperates with the limit hole 1717. When the limit hole 1717 cooperates with the limit pin 1712, the lead screw 1714 cannot be moved. Rotate, at this time, rotating the handwheel 1713 can realize the lifting and lowering movement of the screw 1714, and realize the up and down movement of the reaction container 173 in the opening on the second support plate 14. When the reaction container 173 is used and needs to be cleaned, the reaction container 173 is adjusted to the bottom of the second support plate 14 and the cooperation between the limit pin 1712 and the limit hole 1717 is cancelled. At this time, rotating the handwheel 1713 can realize the rotation of the screw 1714, thereby realizing the replacement of the reaction container 173 after cleaning with the reaction container 173 that needs to be cleaned (before switching, the first stirring paddle 1581 under the stirring motor 158 can be rinsed with a bottle wash); when the limit pin 1712 is located at the lower end of the strip groove 1711, the reaction container 173 is separated from the second support plate 14, and when the limit pin 1712 is located at the upper end of the strip groove 1711, the reaction container 173 is located in the through hole on the second support plate 14.

[0045] The principle of the present invention is:

[0046] The device of the present invention can be used for screening sludge treatment agents, which is helpful for screening out treatment agents with good treatment effects, thereby helping to reduce the amount of sludge.

[0047] When in use, the sludge from the sewage treatment plant is placed in the sludge container 151, and the reagent to be tested is placed in the reagent container. During the process, since the reagents are often used in combination, it is often necessary to start multiple reagent containers at the same time; after adding the reagent to the reagent container, press the exhaust valve on the air pipe in the matching mechanism 162, so that the piston in the annular air chamber contracts, and the spring in the first telescopic support mechanism 1624 pops up and makes the corresponding first matching gear 1615 match with the second matching gear 1616, so that the transmission mechanism 161 can drive the corresponding second stirring paddle 163 in the reagent container to start working; since the sludge container 151 must be set to stir, the sludge container 151 does not need the matching mechanism 162, and one or more reagent containers are selected according to actual needs. When the annular air chamber is inflated, the corresponding second stirring paddle 163 in the reagent container that is not needed will not start working.

[0048] Since the sludge container 151 and the reagent container are only used for mixing the solution, a very high stirring speed is not required, generally 60 to 120 r / min, at which time the transmission mechanism 161 can operate stably.

[0049] The mixed sludge and reagent are transported to the reaction container 173 through the delivery pump 156, and filtered after reaction in the reaction container 173. During the process, the sludge specific resistance can be measured, so as to compare and screen out suitable sludge treatment reagents.

[0050] After one batch of reactions is completed, the reaction container 173 needs to be cleaned and another batch of reactions needs to be started. In the present invention, the lifting and conversion mechanism 17 can lower the reaction container 173 and then rotate the conversion position. Cleaning can be started on one side while experimental operations are performed on the other side, which helps to improve experimental efficiency.

[0051] In the embodiment of the present invention, cleaning can be carried out manually, but for those skilled in the art, using a clean water tank, a pump, a nozzle, etc. to add water during the cleaning process helps to reduce labor intensity and is more convenient for use in experimental operations.

[0052] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A sludge treatment agent screening device, characterized in that: Including batching system, reaction system and cleaning system; The batching system includes a transmission mechanism, a sludge container and a reagent container. The transmission mechanism directly drives the stirring paddle in the sludge container, and the transmission mechanism can selectively drive the stirring paddle in the reagent container through a matching mechanism; the liquid in the sludge container and the reagent container is transported to the reaction system; The reaction system comprises a reaction container, and the liquid in the sludge container and the reagent container is transported to the reaction container, a stirring paddle is arranged in the reaction container, and a suction filter device is arranged below the reaction container, and the suction filter device is connected to a vacuum pump; The cleaning system comprises a reaction container, a cleaning brush is arranged in the reaction container, a beaker container is arranged below the reaction container, and the beaker container cooperates with a sewage tank; a cleaning pipe is arranged at the bottom of the reagent container, a control valve is arranged on the cleaning pipe, and the cleaning pipe cooperates with the sewage tank; The reaction container in the reaction system and the reaction container in the cleaning system are switched with each other through a lifting conversion mechanism.

2. A sludge treatment agent screening device according to claim 1, characterized in that: The transmission mechanism includes a transmission motor, which is connected to a transmission gear and is provided with a driven gear. The transmission gear is transmission-connected to the driven gear through a transmission chain; the transmission chain is transmission-connected to multiple first matching gears at the same time, and each first matching gear is matched with a second matching gear; one of the second matching gears is directly transmission-connected to a stirring paddle in the sludge container; the remaining second matching gears are transmission-connected to a stirring paddle in the reagent container through matching mechanisms respectively.

3. A sludge treatment agent screening device according to claim 2, characterized in that: The matching mechanism includes two transmission members arranged up and down, namely a first transmission member and a second transmission member, the first transmission member is located below the second matching gear and is connected to the second matching gear in transmission, and a first telescopic support mechanism is arranged below the first transmission member; A matching piece is provided, a second transmission piece is located above the matching piece and is transmission-connected to the matching piece, and a second telescopic support mechanism is supported and provided above the second transmission piece; The mating piece and the second mating gear are both fixedly connected to the rotating shaft, and the rotating shaft is connected to the stirring paddle in transmission; when the second telescopic support mechanism is extended, the first telescopic support mechanism is compressed, and the transmission between the first mating gear and the second mating gear is disconnected; when the second telescopic mechanism is contracted, the first telescopic support mechanism is restored, and the first mating gear and the second mating gear resume transmission.

4. A sludge treatment agent screening device according to claim 3, characterized in that: The transmission member includes a first part and a second part, and a through hole is arranged at the center of the first part and the second part, and the through hole cooperates with the rotating shaft; a placement groove is arranged on the first part, and a ball is placed in the placement groove; the second part is detachably fixedly connected to the first part, and a groove is arranged around the second part, and the groove cooperates with the placement groove. When the second part is fixed on the first part, the diameter of the groove is smaller than the diameter of the ball.

5. The sludge treatment agent screening device according to claim 3, characterized in that: The first telescopic support mechanism comprises a spring, a telescopic rod is arranged outside the spring, the telescopic rod comprises an outer tube and an inner tube, and the outer tube is sleeved on the inner tube.

6. The sludge treatment agent screening device according to claim 3, characterized in that: The second telescopic support mechanism includes an annular air chamber, a piston connecting part is arranged around the annular air chamber, a piston is arranged in the piston connecting part, and a piston rod of the piston is fixedly connected to the second transmission member; one side of the annular air chamber is connected to the inflation ball through an air pipe, and an exhaust valve is arranged on the air pipe.

7. The sludge treatment agent screening device according to claim 1, characterized in that: The lifting conversion mechanism comprises a mechanism box, the mechanism box is connected with a connecting rod, and the connecting rod is respectively connected with a reaction container in the reaction system and a reaction container in the cleaning system.

8. The sludge treatment agent screening device according to claim 7, characterized in that: The mechanism box includes an upper part and a lower part. A worm wheel is arranged in the upper part, the worm wheel cooperates with the worm, and the worm is connected to the handwheel outside the upper part; the worm wheel is threadedly connected to the lead screw through a thread at the center of the worm wheel, the upper end of the lead screw is connected to the connecting rod, and the lower end of the lead screw extends to the lower part. A limiting hole is arranged at the lower end of the lead screw, and a strip groove is arranged on the outer side wall of the lower part. A limiting pin is inserted in the strip groove, and the limiting pin cooperates with the limiting hole.

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