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A hydraulic pump includes a housing, a seat portion, and a valve element. The housing has a compression chamber and a fluid passage. The seat portion is provided midway through the fluid passage. The valve element is located between the compression chamber and the fluid passage. The valve element is

A hydraulic pump includes a housing, a seat portion, and a valve element. The housing has a compression chamber and a fluid passage. The seat portion is provided midway through the fluid passage. The valve element is located between the compression chamber and the fluid passage. The valve element is a closed-end cylindrical member having a bottom portion, a cylindrical portion, and an opening end arranged in this order. The cylindrical portion is located farther away from the seat portion than the bottom portion. The valve element is seated to the seat portion at the bottom portion. A stopper substantially closes the opening end when making contact with the opening end to regulate movement of the valve element.

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1. A hydraulic pump comprising: a housing having a compression chamber and a fluid passage;a seat portion provided midway through the fluid passage;a valve element located between the compression chamber and the fluid passage to control communication therebetween through a communication channel by b

1. A hydraulic pump comprising: a housing having a compression chamber and a fluid passage;a seat portion provided midway through the fluid passage;a valve element located between the compression chamber and the fluid passage to control communication therebetween through a communication channel by being lifted from and seated to the seat portion, the valve element being substantially a plate-shaped member;a solenoid actuator provided upstream of the valve element with respect to fluid flow for manipulating the valve element by lifting the valve element from the seat portion; anda stopper configured to make contact with an end of the valve element to regulate movement of the valve element in a direction opposite to the seat portion,wherein the communication channel is defined between the housing and an outer circumferential periphery of the stopper,the stopper is a closed-end cylindrical member having a bottom portion being closed to fluid, a cylindrical portion extending from an outer circumferential periphery of the bottom portion, and an opening end defined by the cylindrical portion, the bottom portion and the opening end being located at opposite axial ends of the cylindrical portion, the bottom portion being located farther away from the valve element than the cylindrical portion, andthe opening end is configured to make contact with the end of the valve element. 2. The hydraulic pump according to claim 1, further comprising: a resilient member accommodated in the stopper,wherein the resilient member is in contact with the bottom portion at one end and in contact with the valve element at an other end to bias the valve element toward the seat portion. 3. The hydraulic pump according to claim 1, wherein the solenoid actuator includes a needle, a first biasing member, and a coil,the first biasing member is configured to bias the valve element via the needle so as to lift the valve element from the seat portion, andthe coil is configured to attract the needle in a direction opposite to the valve element. 4. The hydraulic pump according to claim 1, wherein the valve element has a communication passage configured to communicate the communication channel with an interior of the cylindrical portion. 5. The hydraulic pump according to claim 1, wherein the stopper has a communication passage configured to communicate the communication channel with an interior of the cylindrical portion. 6. The hydraulic pump according to claim 3, further comprising: a first suspending member located farther away from the valve element than the stopper, the first suspending member being fixed to an inner wall of the housing; anda second biasing member located further away from the valve element than the stopper and configured to bias the stopper in a direction opposite to the valve element so as to suspend the stopper on the first suspending member. 7. The hydraulic pump according to claim 3, further comprising: a second biasing member located further away from the valve element than the stopper,wherein the housing has an inner wall having a step portion located radially outside of the cylindrical portion, andthe second biasing member is configured to bias the stopper toward the valve element so as to suspend the stopper on the step portion. 8. The hydraulic pump according to claim 6, further comprising: a second suspending member located further away from the valve element than the stopper,wherein the second suspending member being configured to suspend an end portion of the second biasing member on an opposite side of the valve element. 9. The hydraulic pump according to claim 7, further comprising: a suspending member located further away from the valve element than the stopper,wherein the suspending member is configured to suspend an end portion of the second biasing member on an opposite side of the valve element.