Device for delivering liquid at a stable flow rate
A liquid delivery device includes a constant flow valve, a pump and channels. A medicinal solution bag is connected to the liquid delivery device. The pump has a suction aperture, a discharge aperture and check valves. The constant flow valve includes a valve casing and a diaphragm that partitions the interior of the valve casing to form a first valve chamber and a second valve chamber. A first opening, a second opening, and a third opening are provided in the valve casing. A conical spring arranged between and in contact with a top plate and the diaphragm is provided in the second valve chamber. The spring applies a pressure towards an O-ring side to a second main surface of the diaphragm.
1. A liquid delivery device comprising:
a pump having a suction aperture and a discharge aperture;
a liquid consumption unit; and
a valve including:
a bottom plate with a first opening communicatively coupled to the discharge aperture, such that a liquid from the discharge aperture flows into the valve via the first opening, and a second opening communicatively coupled to the liquid consumption unit, such that the liquid flows out from the valve via the second opening to the liquid consumption unit;
a valve seat disposed around a periphery of the first opening or the second opening;
a top plate with a third opening in fluid communication with air outside the liquid delivery device;
a diaphragm that is disposed between the bottom plate and the top plate and that includes a first main surface that faces the bottom plate and a second main surface that faces the top plate, such that the diaphragm and the bottom plate of the valve form a first valve chamber and the top plate and the diaphragm form a second valve chamber; and
a pressure-applying member disposed between the top plate and the diaphragm to apply pressure on the second main surface of the diaphragm,
wherein:
a region of the first main surface of the diaphragm in communication with the first opening has an area S P ,
the second main surface of the diaphragm has an area S S ,
the pump has a discharge pressure P 1 when a discharge flow rate of the pump is zero,
a pressure P S is applied to the second main surface of the diaphragm by the pressure-applying member,
a pressure P O is applied to a region of the first main surface of the diaphragm that is continuous with the second opening, and
wherein 1<α≦βγ−γ+1 in a range 0≦P O <P S , where α equals S S /S P (α>1), β equals P 1 /P S (β>1), and γ % is a flow rate accuracy.
2. The liquid delivery device according to claim 1 , wherein the flow rate accuracy γ % is 10%.
3. The liquid delivery device according to claim 1 , wherein the pressure-applying member includes an adjustment mechanism to adjust the pressure applied to the second main surface of the diaphragm.
4. The liquid delivery device according to claim 3 , wherein the adjustment mechanism includes an elastic body and a pressing body that urges the elastic body toward the valve seat.
5. The liquid delivery device according to claim 4 , wherein the pressing body is provided in the valve and is rotatable by screwing a screw having a rotational axis in a direction orthogonal to the diaphragm.
6. The liquid delivery device according to claim 5 , wherein rotating the pressing body adjusts the pressure applied to the second main surface of the diaphragm.
7. The liquid delivery device according to claim 1 , wherein the valve seat is a protruding member that is integrated with the diaphragm.
8. The liquid delivery device according to claim 1 , wherein the valve seat is integrated with the bottom plate of the valve.
9. The liquid delivery device according to claim 1 , wherein the pressure-applying member is integrated with the diaphragm.
10. The liquid delivery device according to claim 1 , wherein the valve seat comprises an O-ring.
11. The liquid delivery device according to claim 10 , wherein the O-ring is disposed between the bottom plate and the first main surface of the diaphragm.
12. The liquid delivery device according to claim 11 , wherein the O-ring is disposed around the periphery of the second opening of the bottom plate of the valve.
13. The liquid delivery device according to claim 12 , wherein, when pressure greater than a threshold resulting from the pressure-applying member is applied to the first main surface of the diaphragm, the diaphragm separates from the O-ring such that the first opening is in fluid communication with the second opening of the bottom plate of the valve.
14. The liquid delivery device according to claim 1 , wherein the pressure-applying member is a spring and is disposed in the second valve chamber.
15. The liquid delivery device according to claim 1 , wherein the diaphragm and the bottom plate of the valve form a valve chamber between the first opening and the second opening.
16. The liquid delivery device according to claim 1 , wherein the bottom plate is flat and the first opening and the second opening are disposed adjacent to each other.