I understand that if my flop equity is greater than my fair share that any bets I put in are +EV. But what about on the river? Say I'm in a limit game and my equity 4 handed is 30%, but another player's equity is 51% and the other 2 players make up the rest. Now, if I put in a bet (and everyone just calls) I have a +EV situation, but there is a good chance that the villain with 51% equity will put in a raise if I do so and for the sake of this argument I cannot fold if raised by villain.

It feels wrong not to bet and risk it checking around when we have 2 possible callers with virtually no equity in the hand and my equity is greater than 25%, but it also feels wrong betting into a player whose equity is greater than ours and risk being raised. How to find the balance here? Thanks.

People use "EV" and "equity" in two distinct ways (to be more accurate, some people use them in inconsistent ways that blend the distinction inappropriately).

The first is a hard mathematical number you can calculate. If the pot were frozen and the remaining cards dealt out, over and over again, what is the average fraction of the time you would win (equity) or what is your average profit (EV)?

The second is a number that depends on assumptions about current state and future events. How much would you sell your position in the hand for at this moment?

For example, you hold Js Ts preflop and the other hands are Ah Qc, Kc Qd and 8h 8c. You have 28% equity if the hand were dealt out, so if you bet $100 and it gets called by the other four players, you gain $12 of EV in the first sense. In the second sense, you'd have to consider the possible hands the other players might be holding, not just the cards they have, plus the possible ways the hand might play out. In this case you might like your situation because there are lots of ways for you to win a big pot with a straight or a flush, or a small one with a J or T or two, and there aren't many ways that you'll put in a lot of money in a losing cause.

To get to your specific question, it depends on more than just the equity, it depends on what other people know. But to keep it simple, suppose everyone in the hand knows exactly which of the 44 unseen cards on the will win for each player. 13 win for you, 22 for A, 4 for B and 5 for C. Of course, in this situation, there can't be any river betting.

While you would gain EV if you bet on the turn and everyone called, that won't happen. A will bet the pot, forcing B and C to fold, after which you have to fold. Position doesn't matter, you know B and C will fold.

In real poker, it's more complicated. One important consideration is who gets B and C's equity if they fold? If you win if nobody improves, then B and C folding brings your equity up to 50%, so you should clearly bet. But if A wins if nobody improves then B and C folding doesn't help you. Here you generally will not bet, although there are situations where it makes sense, depending on what others think about the hand and how they will react. But it will not be a value bet, a bet made to increase equity, it will be some form of strategic bet.