In this task, you are given a sentence or phrase in Xhosa. You must translate it to English in a way that is equivalent in terms of meaning and grammatically correct.

Example input: Ulwakhiwo neempawu zentsinga zemifuno.
Example output: Construction and characteristics of vegetable fibre cordage.
Example explanation: 'Ulwakhiwo neempawu' means construction/make-up and characteristics, 'zentsinga zemifuno' roughly translates to 'of fibre from vegetables'.
Q: Isivalo esenzelwe ukuvumela ukuba ulwelo luhambe kwicala elinye, kwaye singamvumeli naluphi na ulwelo ukubalubuyele okanye lungene kwelinye icala laso .
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
a valve which is designed to allow fluid to pass through the valve in one direction, but not allow any fluid to either return and flow through the valve in the other direction