If it slowly drops and does not run out through test cock No. 3, then No. 2 ball valve has a small leak, but No. 2 check valve is tight.

• 如果水柱慢慢下降，并且没有从测试旋塞3号流出，则2号球阀有点泄漏，但是2号止回阀密封紧密。